The molecular basis of a significant number of cases of isolated growth hormone deficiency remains unknown. We describe three sisters affected with severe isolated growth hormone deficiency and pituitary hypoplasia caused by biallelic mutations in the RNPC3 gene, which codes for a minor spliceosome protein required for U11/U12 small nuclear ribonucleoprotein (snRNP) formation and splicing of U12‐type introns. We found anomalies in U11/U12 di‐snRNP formation and in splicing of multiple U12‐type introns in patient cells. Defective transcripts include preprohormone convertases SPCS2 and SPCS3 and actin‐related ARPC5L genes, which are candidates for the somatotroph‐restricted dysfunction. The reported novel mechanism for familial growth hormone deficiency demonstrates that general mRNA processing defects of the minor spliceosome can lead to very narrow tissue‐specific consequences ...
During spliceosome assembly, protein-protein interactions (PPI) are sequentially formed and disrupted to accommodate the spatial requirements of pre-mRNA substrate recognition and catalysis. Splicing activators and repressors, such as SR proteins and hnRNPs, modulate spliceosome assembly and regulate alternative splicing. However, it remains unclear how they differentially interact with the core spliceosome to perform their functions. Here, we investigate the protein connectivity of SR and hnRNP proteins to the core spliceosome using probabilistic network reconstruction based on the integration of interactome and gene expression data. We validate our model by immunoprecipitation and mass spectrometry of the prototypical splicing factors SRSF1 and hnRNPA1. Network analysis reveals that a factors properties as an activator or repressor can be predicted from its overall connectivity to the rest of the spliceosome. In addition, we discover and experimentally validate PPIs between the oncoprotein SRSF1 and
Two types of spliceosomes catalyze splicing of pre-mRNAs. The major U2-type spliceosome is found in all eukaryotes and removes U2-type introns, which represent more than 99% of pre-mRNA introns. The minor U12-type spliceosome is found in some eukaryotes and removes U12-type introns, which are rare and have distinct splice consensus signals. The U12-type spliceosome consists of several small nuclear RNAs and associated proteins. This gene encodes a 65K protein that is a component of the U12-type spliceosome. This protein contains two RNA recognition motifs (RRMs), suggesting that it may contact one of the small nuclear RNAs of the minor spliceosome. [provided by RefSeq, Jul 2008 ...
The current model of spliceosome assembly was developed principally from the in vitro pattern of small nuclear ribonucleoprotein (snRNP) particle association with synthetic splicing substrates (reviewed in Moore et al., 1993; Madhani and Guthrie, 1994; Krämer, 1996). In mammals and yeast, spliceosome assembly progresses by the sequential addition of the U1 snRNP→U2 snRNP→U4/U6.U5 tri‐snRNP particles to the pre‐mRNA. Before 5′ splice‐site cleavage (chemical step I in splicing), the affinities of the U1 and U4 snRNAs for the splicing complex are greatly reduced and, under many (Pikielny et al., 1986; Cheng and Abelson, 1987; Konarska and Sharp, 1987) although not all (Blencowe et al., 1989) isolation conditions, the U4 snRNA is lost from the spliceosome. This model of spliceosome assembly is supported by the abridged spliceosome assembly profiles observed when splicing is inhibited by specific mutations in the pre‐mRNA or when one of the many trans‐acting components of splicing is ...
Assembly of the spliceosome by the stepwise binding of the snRNPs to the pre-mRNA. In the early phase of spliceosome assembly, the U1 snRNP binds to the 5 splice site (5 SS: where exon 1 ends and the intron begins), and the U2 snRNP binds to the so-called branch point (BP: near the 3 end of the intron). This spliceosome assembly intermediate is called the A complex. The subsequent binding of the U4/U6.U5 tri snRNP complex gives rise to the precatalytic B complex. The catalytic activation of the spliceosome takes place in two steps. In the first, the RNA helicase Brr2 acts to produce the Bact complex and in the second, the RNA helicase Prp2 facilitates the formation of the B* complex. This has a functional active site and, following the recruitment of the protein Cwc25, the first step of splicing takes place. In this step, the phosphodiester bond at the 5 splice site is cleaved and, at the same time, the 5 end of the intron becomes linked to the 2 hydroxyl group of an adenosine at the ...
Nuclear pre-mRNA splicing takes places in a large RNP complex, the spliceosome, which is assembled in an ordered multistep process. It consists of five small nuclear RNAs (the U1, U2, U4, U5, and U6 snRNAs) and more than 100 proteins, as recent proteomic analyses have determined (15, 16, 39). The spliceosome shows characteristic dynamics during assembly and splicing catalysis. For example, only the U2, U5, and U6 snRNAs participate in the catalytic center of the spliceosome, whereas the U1 and U4 snRNAs play essential roles only during the early assembly stages. After completion of the two-step splicing reaction and the release of mRNA and lariat products, the spliceosome disassembles into its components. Before entering a new cycle, at least some the components presumably must be reactivated. However, very little is known about this recycling phase of the spliceosome cycle.. The U4, U5, and U6 snRNAs enter the prespliceosome in the form of the 25S U4/U6.U5 tri-snRNP but are released from the ...
Mutations of spliceosome components are common in myeloid neoplasms. One of the affected genes, PRPF8, encodes the most evolutionarily conserved spliceosomal protein. We identified either recurrent somatic PRPF8 mutations or hemizygous deletions in 15/447 and 24/450 cases, respectively. Fifty percent of PRPF8 mutant and del(17p) cases were found in AML and conveyed poor prognosis. PRPF8 defects correlated with increased myeloblasts and ring sideroblasts in cases without SF3B1 mutations. Knockdown of PRPF8 in K562 and CD34+ primary bone marrow cells increased proliferative capacity. Whole-RNA deep sequencing of primary cells from patients with PRPF8 abnormalities demonstrated consistent missplicing defects. In yeast models, homologous mutations introduced into Prp8 abrogated a block experimentally produced in the second step of the RNA splicing process, suggesting that the mutants have defects in proof-reading functions. In sum, the exploration of clinical and functional consequences suggests that PRPF8
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Precursor mRNA (pre-mRNA) splicing is catalyzed by a large ribonucleoprotein complex known as the spliceosome. Numerous studies have indicated that aberrant splicing patterns or mutations in spliceosome components, including the splicing factor 3b subunit 1 (SF3B1), are associated with hallmark cancer phenotypes. This has led to the identification and development of small molecules with spliceosome-modulating activity as potential anticancer agents. Jerantinine A (JA) is a novel indole alkaloid which displays potent anti-proliferative activities against human cancer cell lines by inhibiting tubulin polymerization and inducing G2/M cell cycle arrest. Using a combined pooled-genome wide shRNA library screen and global proteomic profiling, we showed that JA targets the spliceosome by up-regulating SF3B1 and SF3B3 protein in breast cancer cells. Notably, JA induced significant tumor-specific cell death and a significant increase in unspliced pre-mRNAs. In contrast, depletion of endogenous SF3B1 ...
This is a pretty good article on the origin of the spliceosome from self-splicing introns: Vosseberg J, Snel B. Domestication of self-splicing introns during eukaryogenesis: the rise of the complex spliceosomal machinery. Biol Direct. 2017 Dec 1;12(1):30. DOI:10.1186/s13062-017-0201-6 There are many interesting references given in that article also, for example on spliceosomal diversity. There are simple protozoan parasites known with as few as 27 introns in their entire genomes, and highly s...
Knockdown of several components of the spliceosome results in premature loss of SCC, thus preventing the stable attachment of microtubules and the bi‐orientation of chromatids (van der Lelij et al, 2014; Sundaramoorthy et al, 2014; Watrin et al, 2014). Some of these factors, such as SNW1 (a component of a NTC‐related subcomplex), PRPF8 (a key coordinator of splicing catalysis associated with U5 snRNP) or MAFP1 (which associates transiently in the context of spliceosomal rearrangements previous to catalysis), are believed to have core functions in the splicing process. Their impact on cell division, however, raised the possibility that they display specific functions in mitotic progression different from splicing (Hofmann et al, 2010). To address this issue, Petronczki and colleagues analyzed in detail a set of 33 spliceosome components previously reported to alter mitosis when downregulated (Neumann et al, 2010). In this new study, knockdown of 26 out of these 33 splicing factors tested ...
Akerman, M., Fregoso, O. I., Das, S., Ruse, C., Jensen, M. A., Pappin, D. J., Zhang, M. Q., Krainer, A. R. (2015) Differential connectivity of splicing activators and repressors to the human spliceosome. Genome Biol, 16 (1). p. 119. ISSN 1465-6914 (Electronic)1465-6906 (Linking) Anczukow, O., Krainer, A. R. (2015) The spliceosome, a potential Achilles heel of MYC-driven tumors. Genome Med, 7 (1). p. 107. ISSN 1756-994X (Electronic)1756-994X (Linking) ...
The PDB archive contains information about experimentally-determined structures of proteins, nucleic acids, and complex assemblies. As a member of the wwPDB, the RCSB PDB curates and annotates PDB data according to agreed upon standards. The RCSB PDB also provides a variety of tools and resources. Users can perform simple and advanced searches based on annotations relating to sequence, structure and function. These molecules are visualized, downloaded, and analyzed by users who range from students to specialized scientists.
Significant advances have been made in elucidating the biogenesis pathway and three-dimensional structure of the UsnRNPs, the building blocks of the spliceosome. U2 and U4/U6*U5 tri-snRNPs functionally associate with the pre-mRNA at an earlier stage of spliceosome assembly than previously thought, a …
Bertram, K.; Agafonov, D. E.; Dybkov, O.; Haselbach, D.; Leelaram, M. N.; Will, C. L.; Urlaub, H.; Kastner, B.; Lührmann, R.; Stark, H.: Cryo-EM structure of a pre-catalytic human spliceosome primed for activation. Cell 170 (4), pp. 701 - 713, e1 - e4 (2017 ...
The removal of introns from pre-mRNA transcripts is an essential step in the expression of almost all human genes. we are collaborating with several groups to d...
Genes in eukaryotic organisms are frequently interrupted by non-coding segments called introns. Before the protein can be produced, the entire length of each gene including the introns, is transcribed to produce precursor messenger RNA (pre-mRNA).
infinity-imagined: The interior of a Eukaryotic Cell, from the outer membrane through the cytosol to the nucleus. All molecular structures are colored by their function; the cytoskeleton is blue, membranes are green, ribosomes are purple, RNA and spliceosomes are pink, DNA and nucleosomes are yellow. This cell is producing antibodies, all steps of the process…
Complete information for CWC25 gene (Protein Coding), CWC25 Spliceosome Associated Protein Homolog, including: function, proteins, disorders, pathways, orthologs, and expression. GeneCards - The Human Gene Compendium
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Pre-mRNA splicing is executed by the spliceosome, which has eight major functional states each with distinct composition. Five of these eight human spliceosomal complexes, all preceding exon ligation, have been structurally characterized. In this study, we report the cryo-electron microscopy structures of the human post-catalytic spliceosome (P complex) and intron lariat spliceosome (ILS) at average resolutions of 3.0 and 2.9 Å, respectively. In the P complex, the ligated exon remains anchored to loop I of U5 small nuclear RNA, and the 3-splice site is recognized by the junction between the 5-splice site and the branch point sequence. The ATPase/helicase Prp22, along with the ligated exon and eight other proteins, are dissociated in the P-to-ILS transition. Intriguingly, the ILS complex exists in two distinct conformations, one with the ATPase/helicase Prp43 and one without. Comparison of these three late-stage human spliceosomes reveals mechanistic insights into exon release and spliceosome ...
References Mansfield SG, Chao H, Walsh CE. RNA repair using spliceosome-mediated RNA trans-splicing. Trends Mol Med. 2004 Jun;10(6):263-8. (...)
In previous studies, we reported that fractionation of HeLa cell nuclear extracts on glycerol gradients revealed an endogenous ∼10S particle that contained galectin-3 and U1 snRNP and this particle was sufficient to load the galectin polypeptide onto a pre-mRNA substrate. We now document that this interaction between the galectin-3-U1 snRNP particle and the pre-mRNA results in a productive spliceosomal complex, leading to intermediates and products of the splicing reaction. Nuclear extracts were depleted of U1 snRNP with a concomitant loss of splicing activity. Splicing activity in the U1-depleted extract can be reconstituted by the galectin-3-U1 snRNP particle, isolated by immunoprecipitation of the 10S region (fractions 3-5) of the glycerol gradient with anti-galectin-3 antibodies. In contrast, parallel anti-galectin-3 immunoprecipitation of free galectin-3 molecules not in a complex with U1 snRNP (fraction 1 of the same gradient), failed to restore splicing activity. These results indicate ...
Involved in both the assembly of spliceosomal snRNPs and the methylation of Sm proteins (PubMed:21081503, PubMed:18984161). Chaperone that regulates the assembly of spliceosomal U1, U2, U4 and U5 small nuclear ribonucleoproteins (snRNPs), the building blocks of the spliceosome. Thereby, plays an important role in the splicing of cellular pre-mRNAs. Most spliceosomal snRNPs contain a common set of Sm proteins SNRPB, SNRPD1, SNRPD2, SNRPD3, SNRPE, SNRPF and SNRPG that assemble in a heptameric protein ring on the Sm site of the small nuclear RNA to form the core snRNP. In the cytosol, the Sm proteins SNRPD1, SNRPD2, SNRPE, SNRPF and SNRPG are trapped in an inactive 6S pICln-Sm complex by the chaperone CLNS1A that controls the assembly of the core snRNP. Dissociation by the SMN complex of CLNS1A from the trapped Sm proteins and their transfer to an SMN-Sm complex triggers the assembly of core snRNPs and their transport to the nucleus. May also indirectly participate in cellular volume control by activation
Plays role in pre-mRNA splicing as core component of the SMN-Sm complex that mediates spliceosomal snRNP assembly and as component of the spliceosomal U1, U2, U4 and U5 small nuclear ribonucleoproteins (snRNPs), the building blocks of the spliceosome. Component of both the pre-catalytic spliceosome B complex and activated spliceosome C complexes. Is also a component of the minor U12 spliceosome (By similarity). As part of the U7 snRNP it is involved in histone pre-mRNA 3-end processing (PubMed:19470752).
Most metazoan genes have multiple exons that must be carefully excised (from the pre-mRNA) and then ligated (to form the mRNA). This RNA splicing occurs in the nucleus, and upon its completion the mRNA is exported to the cytoplasm for translation. Exon definition complexes and spliceosomes begin to assemble during transcription. Some of these complexes interact with RNAP IIs CTD, and some introns are thus excised before transcription has even terminated.. There is no apparent order in which introns get spliced). Introns do no excise in any particular order, and active transcription (or its termination) is not needed for splicing to occur. However, the rate of transcription elongation through an intron can strongly affect what splice sites are chosen and thus indirectly couple transcription and splicing. Exon definition complexes and spliceosomes begin assembling during RNA synthesis; interaction with RNAP IIs CTD leads to excision of some introns before transcription has even ...
The concept of the gene has been constantly challenged by new discoveries in the life sciences. Recent challenging observations include the high frequency of alternative splicing events and the common transcription of non-protein-coding-RNAs (ncRNAs) from the genome. The latter has long been considered noise in biological systems. Multiple lines of evidence from genomic studies indicate that alternative splicing and ncRNA play important roles in expanding proteome diversity in eukaryotes. Here, the aim is to find the link between alternative splicing and ncRNAs by studying the expression profile of the spliceosomal snRNAs (U snRNA).. Spliceosomal snRNAs are essential for pre-mRNA splicing in eukaryotes. They participate in splice site selection, recruitment of protein factors and catalyzing the splicing reaction. Because of this, both the abundance and diversity of U snRNAs were expected to be large. In our study we deeply analyzed the U snRNA population in primates using a combination of ...
Spliceosome mechanism dissected at the single molecule level ABSTRACT: The spliceosome is a multi-megadalton RNA-protein complex that catalyzes in all eukaryote...
This site contains information about the spliceosomal introns of the yeast Saccharomyces cerevisiae. Introns present special problems for the annotation of eukaryotic genomes. Splice sites are information-poor, and their recognition by the splicing apparatus is highly context-dependent and regulated, making identification by computational gene prediction programs a challenge. At present we do not understand splice site context well enough to predict which potential splice sites will be used, and thus how the genomic sequences will be expressed. Understanding the how and why of introns will require genome level information about splicing. One element of this will involve understanding splicing patterns and how they are regulated globally. Another element will involve understanding how splicing patterns change during evolution. To begin we study yeast, since it has the simplest known eukaryotic genome. In these pages we have listed known spliceosomal introns in the yeast genome and documented the ...
To estimate absolute protein contents in complex mixtures, we previously defined a protein abundance index (PAI) as the number of observed peptides divided by the number of observable peptides per protein (Rappsilber, J., Ryder, U., Lamond, A. I., and Mann, M. (2002) Large-scale proteomic analysis of the human spliceosome. Genome. Res. 12, 1231-1245). Here we report that PAI values obtained at different concentrations of serum albumin show a linear relationship with the logarithm of protein concentration in LC-MS/MS experiments. This was also the case for 46 proteins in a mouse whole cell lysate. For absolute quantitation, PAI was converted to exponentially modified PAI (emPAI), equal to 10PAI minus one, which is proportional to protein content in a protein mixture..... ...
This gene encodes subunit 1 of the splicing factor 3b protein complex. Splicing factor 3b, together with splicing factor 3a and a 12S RNA unit, forms the U2 small nuclear ribonucleoproteins complex (U2 snRNP). The splicing factor 3b/3a complex binds pre-mRNA upstream of the introns branch site in a sequence independent manner and may anchor the U2 snRNP to the pre-mRNA. Splicing factor 3b is also a component of the minor U12-type spliceosome. The carboxy-terminal two-thirds of subunit 1 have 22 non-identical, tandem HEAT repeats that form rod-like, helical structures. Alternative splicing results in multiple transcript variants encoding different isoforms. [provided by RefSeq, Jul 2008 ...
Burge, C. B., Tuschl, T. and Sharp, P.A. Splicing of precursors to mRNAs by the spliceosomes. In RNA World II, R. Gesteland, T. Cech, and J. Atkins, eds., Cold Spring Harbor Laboratory Press, NY, pp. 525-560 (1999) Dredge BK, Polydorides AD, Darnell RB. The splice of life: alternative splicing and neurological disease. Nat Rev Neurosci. 2001 Jan;2(1):43-50. Hastings ML, Krainer AR. Pre-mRNA splicing in the new millennium. Curr Opin Cell Biol. 2001 Jun;13(3):302-9. Maniatis T, Reed R. An extensive network of coupling among gene expression machines. Nature. 2002 Apr 4;416(6880):499-506. Nilsen, T.W. RNA/RNA interactions in nuclear pre-mRNA splicing. In: RNA Structure and Function. R. Simons and M. Grunberg-Manago eds., Cold Spring Harbor Laboratory Press, NY, pp. 279-307 (1998). Staley JP, Guthrie C. Mechanical devices of the spliceosome: motors, clocks, springs, and things. Cell. 1998 Feb 6;92(3):315-26. Tollervey D, Caceres JF. RNA processing marches on. Cell. 2000 Nov 22;103(5):703-9. ...
The sequencing of eukaryotic genomes revealed that a remarkably small fraction is occupied by protein-coding sequences (2% in human). Surprisingly, protein-coding sequences occupy a similarly small percentage of the total diversity of transcriptional output. The genome generates incredibly complex populations of non-coding RNAs. What is the role of these non-coding RNAs? Over the past decade, it has become clear that small regulatory RNAs are key regulators of multiple biological processes, including transcription, translation and mRNA stability. Many non-coding RNAs such as ribosomal and spliceosomal RNAs are well known, and these act at key steps of gene expression. Others, like the recently discovered miRNAs modulate gene expression by regulating stability and translation of multiple protein-coding mRNAs. But even beyond these known non-coding RNAs, there is a vast number of species still awaiting characterization. We are interested in identifying and dissecting the role of other, less ...
Excision, or splicing, of noncoding regions (introns) from precursor (pre)-mRNA in eukaryotes is catalyzed by the spliceosome, a ribonucleoprotein complex comprising recyclable small nuclear (sn)RNA and protein components. An early step in assembly of th
My main interest is to study biology at the level of its macromolecular machines and to gain a quantitative biophysical understanding of how these machines drive important cell biological processes. Since new tools enable new biology, I also develop advanced microscopy methods that aim to overcome the limitations of current methods and help us visualize the macromolecular machineries of the cell in action with high spatiotemporal resolution. Specifically, I am interested in the molecular machinery involved in two fundamental biological processes: transport machinery that drives intracellular trafficking of vesicles and transcriptional machinery that drives gene expression. At the heart of and common to both biological problems is the interaction of multiple proteins with each other and with other proteins to form functional macromolecular nanoscopic complexes. The spatial and temporal organization of these interactions is tightly regulated and the failure to form these macromolecular complexes ...
Molecular medicine of the Golabi-Ito-Hall Syndrome. A point-mutation in the PQBP1 human gene leads to a missense translation of the protein. PQBP1 may lose the ability to recruite some splicing factors, like SIPP1, to the activated B spliceosome complex ...
Multiscale simulation of DNA, Dans, Pablo D., Walther Jurgen, Gómez Hansel, and Orozco Modesto , Current Opinions in Structural Biology - Theory and simulation • Macromolecular machines 2016, 02/2016, Volume 37, p.29 - 45, (2016) ...
Multiscale simulation of DNA, Dans, Pablo D., Walther Jurgen, Gómez Hansel, and Orozco Modesto , Current Opinions in Structural Biology - Theory and simulation • Macromolecular machines 2016, 02/2016, Volume 37, p.29 - 45, (2016) ...
Multiscale simulation of DNA, Dans, Pablo D., Walther Jurgen, Gómez Hansel, and Orozco Modesto , Current Opinions in Structural Biology - Theory and simulation • Macromolecular machines 2016, 02/2016, Volume 37, p.29 - 45, (2016) ...
Component of the spliceosomal U1 snRNP, which is essential for recognition of the pre-mRNA 5 splice-site and the subsequent assembly of the spliceosome. SNRNP70 binds to the loop I region of U1-snRNA. The truncated isoforms cannot bind U1-snRNA ...
The spliceosome found in human cells is made up of many different subunits, which must be assembled onto the mRNA precursor in a series of carefully choreographed steps. The binding specificity of individual subunits is crucial for both spliceosome assembly and function. "The assembly factor we have studied, called the U2 Auxiliary Factor or U2AF for short, is critical for the correct recognition of the splicing sites at one end of the introns," says Lena Voithenberg, first author of the new paper. U2AF itself is made up of two different subunits. In its free form, the larger of the two is a highly dynamic protein, as Voithenberg and her colleagues demonstrated by means of single-molecule fluorescence microscopy. Experiments using nuclear magnetic resonance (NMR) spectroscopy carried out in parallel at the Bavarian Center for NMR (run jointly by the Helmholtz Zentrum München and the TUM) provided further information relating to the structure and conformational dynamics of U2AF. ...
The NineTeen complex (NTC) is required for intron removal during splicing. Num1 is a conserved NTC component in Ustilago maydis. It is required for polarized growth of fungal hyphae and affects numerous NTC functions, particularly splicing is influenced on a global scale. Num1 interacting proteins include proteins with functions during trafficking like the Kin1 motor-protein, implicating novel connections between splicing and cytoplasmic transport processes ...
The protein encoded by this gene belongs to the CDC2-like protein kinase (CLK) family. This protein kinase can interact with and phosphorylate the serine- and arginine-rich (SR) proteins, which are known to play an important role in the formation of spliceosomes, and thus may be involved in the regulation of alternative splicing. Studies in the Israeli sand rat Psammomys obesus suggested that the ubiquitin-like 5 (UBL5/BEACON), a highly conserved ubiquitin-like protein, may interact with and regulate the activity of this kinase. Multiple alternatively spliced transcript variants have been observed, but the full-length natures of which have not yet been determined ...
START] From their origin, eukaryotes were complex. They had introns (& complex spliceosomes - half of whose 78 proteins are unique to eukaryotes - to handle them), mitosomes, hydrogenosomes, mitochondria, nuclei, nucleoli, the Golgi apparatus, centrioles, & an endoplasmic reticulum, along with "hundreds of proteins with no orthologs evident in the genomes of prokaryotes ...
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Ribosome biogenesis is a highly complex process that requires several cofactors, including DExD/H-box RNA helicases (RHs). RHs are a family of ATPases that rearrange the secondary structures of RNA and thus remodel ribonucleoprotein (RNP) complexes. DExD/H-box RHs are found in most organisms and play critical roles in a variety of RNA-involved cellular events. In human and yeast cells, many DExD/H box RHs participate in multiple steps of ribosome biogenesis and regulate cellular proliferation and stress responses. In plants, several DExD/H-box RHs have been demonstrated to be associated with plant development and abiotic and biotic stress tolerance through their functions in modulating pre-rRNA processing. In this review, we summarize the pleiotropic roles of DExD/H-box RHs in rRNA biogenesis and other biological functions. We also describe the overall function of the DExD/H-box RH family in ribosome biogenesis based on data from human and yeast.
Pre-mRNA splicing takes place in an RNA machine known as the spliceosome, which consists of small nuclear ribonucleoprotein particles (snRNPs)1 and non-snRNP protein factors. The RNA components in the spliceosome form the catalytic core through a series of dynamic RNA-RNA interactions which are likely to be mediated and/or stabilized by non-snRNP protein factors (for recent reviews see Nilsen, 1998; Staley and Guthrie, 1998). Among the best characterized non-snRNP splicing factors are SR proteins which contain one or two RNA recognition motifs and a signature RS domain containing multiple serine and arginine repeats (for reviews see Fu, 1995; Manley and Tacke, 1996). The RNA recognition motifs bind to RNA sequences in a coordinated fashion to determine splicing specificity (Chandler et al., 1997) and commit pre-mRNA substrates to the splicing pathway (Fu, 1993), whereas the RS domains mediate specific protein- protein interactions in a number of spliceosomal assembly steps (Wu and Maniatis, ...