Identification of a novel domain shared by putative components of the endocytic and cytoskeletal machinery.
We have identified a approximately 140 amino acid domain that is shared by a variety of proteins in budding and fission yeast, nematode, rat, mouse, frog, oat, and man. Typically, this domain is located within 20 residues of the N-terminus of the various proteins. The percent identity among the domains in the 12 proteins ranges from 42 to 93%, with 16 absolutely conserved residues: N-x(11-13)-V-x2-A-T-x(34-36)-R-x(7-8)-W-R-x3-K-x12-G-x-E-x15 -L-x11-12-D-x-G-R-x11-D-x7-R. Even though these proteins share little beyond their segment of homology, data are emerging that several of the proteins are involved in endocytosis and or regulation of cytoskeletal organization. We have named this protein segment the ENTH domain, for Epsin N-terminal Homology domain, and hypothesize that it is a candidate for binding specific ligands and/or enzymatic activity in the cell. (+info)
Reconstitution of a bacterial/plant polyamine biosynthesis pathway in Saccharomyces cerevisiae.
Polyamine synthesis in most organisms is initiated by the decarboxylation of ornithine to form putrescine via ornithine decarboxylase (ODC). Plants, some bacteria and some fungi and protozoa generate putrescine from arginine, via arginine decarboxylase (ADC) and agmatine ureohydrolase (AUH) or agmatine iminohydrolase. A polyamine-requiring strain of Saccharomyces cerevisiae with a mutation in the gene encoding ODC was transformed with plasmids bearing genes encoding Escherichia coli ADC and AUH. Transformants regained the ability to grow in the absence of exogenous polyamines and contained enzyme activities consistent with the presence of both prokaryotic enzymes. Similar results were obtained when a plasmid containing a gene encoding oat (Avena sativa L.) ADC was substituted for the E. coli gene. These data demonstrate the successful complementation of a yeast biosynthetic polyamine synthesis defect by genes encoding an alternative pathway found in bacteria; they also show that plant ADC can substitute for the bacterial enzyme in this pathway. The recombinant yeast provides a tool for the study of the functional properties of these enzymes and for discovery of compounds that specifically inhibit this pathway. (+info)
Mass spectrometric characterization of oat phytochrome A: isoforms and posttranslational modifications.
At least four mRNAs for oat phytochrome A (phyA) are present in etiolated oat tissue. The complete amino acid sequences of two phyA isoforms (A3 and A4) and the N-terminal amino acid sequence of a third isoform (A5) were deduced from cDNA sequencing (Hershey et al., 1985). In the present study, heterogeneity of phyA on a protein level was studied by tryptic mapping using electrospray ionization mass-spectrometry (ESIMS). The total tryptic digest of iodoacetamide-modified phyA was fractionated by gel filtration chromatography followed by reversed-phase high-performance liquid chromatography. ESIMS was used to identify peptides. Amino acid sequences of the peptides were confirmed or determined by collision-induced dissociation mass spectrometry (CID MS), MS/MS, or by subdigestion of the tryptic peptides followed by ESIMS analysis. More than 97% of the phyA3 sequence (1,128 amino acid residues) was determined in the present study. Mass-spectrometric analysis of peptides unique to each form showed that phyA purified from etiolated oat seedling is represented by three isoforms A5, A3, and A4, with ratio 3.4:2.3:1.0. Possible light-induced changes in phytochrome in vivo phosphorylation site at Ser7 (Lapko VN et al., 1997, Biochemistry 36:10595-10599) as well at Ser17 and Ser598 (known as in vitro phosphorylation sites) were also analyzed. The extent of phosphorylation at Ser7 appears to be the same for phyA isolated from dark-grown and red-light illuminated seedlings. In addition to Ser7, Ser598 was identified as an in vivo phosphorylation site in oat phyA. Ser598 phosphorylation was found only in phyA from the red light-treated seedlings, suggesting that the protein phosphorylation plays a functional role in the phytochrome A-mediated light-signal transduction. (+info)
Isolation, characterization, and avenacin sensitivity of a diverse collection of cereal-root-colonizing fungi.
A total of 161 fungal isolates were obtained from the surface-sterilized roots of field-grown oat and wheat plants in order to investigate the nature of the root-colonizing fungi supported by these two cereals. Fungi were initially grouped according to their colony morphologies and then were further characterized by ribosomal DNA sequence analysis. The collection contained a wide range of ascomycetes and also some basidiomycete fungi. The fungi were subsequently assessed for their abilities to tolerate and degrade the antifungal oat root saponin, avenacin A-1. Nearly all the fungi obtained from oat roots were avenacin A-1 resistant, while both avenacin-sensitive and avenacin-resistant fungi were isolated from the roots of the non-saponin-producing cereal, wheat. The majority of the avenacin-resistant fungi were able to degrade avenacin A-1. These experiments suggest that avenacin A-1 is likely to influence the development of fungal communities within (and possibly also around) oat roots. (+info)
Pigment-free NADPH:protochlorophyllide oxidoreductase from Avena sativa L. Purification and substrate specificity.
The enzyme NADPH:protochlorophyllide oxidoreductase (POR) is the key enzyme for light-dependent chlorophyll biosynthesis. It accumulates in dark-grown plants as the ternary enzyme-substrate complex POR-protochlorophyllide a-NADPH. Here, we describe a simple procedure for purification of pigment-free POR from etioplasts of Avena sativa seedlings. The procedure implies differential solubilization with n-octyl-beta-D-glucoside and one chromatographic step with DEAE-cellulose. We show, using pigment and protein analysis, that etioplasts contain a one-to-one complex of POR and protochlorophyllide a. The preparation of 13 analogues of protochlorophyllide a is described. The analogues differ in the side chains of the macrocycle and in part contain zinc instead of the central magnesium. Six analogues with different side chains at rings A or B are active substrates, seven analogues with different side chains at rings D or E are not accepted as substrates by POR. The kinetics of the light-dependent reaction reveals three groups of substrate analogues with a fast, medium and slow reaction. To evaluate the kinetic data, the molar extinction coefficients in the reaction buffer had to be determined. At concentrations above 2 mole substrate/mole enzyme, inhibition was found for protochlorophyllide a and for the analogues. (+info)
Differential effects of mutations in the chromophore pocket of recombinant phytochrome on chromoprotein assembly and Pr-to-Pfr photoconversion.
Site-directed mutagenesis was performed with the chromophore-bearing N-terminal domain of oat phytochrome A apoprotein (amino acid residues 1-595). Except for Trp366, which was replaced by Phe (W366F), all the residues exchanged are in close proximity to the chromophore-binding Cys321 (i.e. P318A, P318K, H319L, S320K, H322L and the double mutant L323R/Q324D). The mutants were characterized by their absorption maxima, and the kinetics of chromophore-binding and the Pr-->Pfr conversion. The strongest effect of mutation on the chromoprotein assembly, leading to an almost complete loss of the chromophore binding capability, was found for the exchanges of His322 by Leu (H322L) and Pro318 by Lys (P318K), whereas a corresponding alanine mutant (P318A) showed wild-type behavior. The second histidine (H319) is also involved in chromophore fixation, as indicated by a slower assembly rate upon mutation (H319L). For the other mutants, an assembly process very similar to that of the wild-type protein was found. The light-induced Pr-->Pfr conversion kinetics is altered in the mutations H319L and S320K and in the double mutant L323R/Q324D, all of which exhibited a significantly faster I700 decay and accelerated Pfr formation. P318 is also involved in the Pr-->Pfr conversion, the millisecond steps (formation of Pfr) being significantly slower for P318A. Lacking sufficient amounts of W366F, assembly kinetics could not be determined in this case, while the fully assembled mutant underwent the Pr-->Pfr conversion with kinetics similar to wild-type protein. (+info)
The mating-type and pathogenicity locus of the fungus Ustilago hordei spans a 500-kb region.
The fungal pathogen Ustilago hordei causes the covered smut disease of barley and oats. Mating and pathogenicity in this fungus are controlled by the MAT locus, which contains two distinct gene complexes, a and b. In this study, we tagged the a and b regions with the recognition sequence for the restriction enzyme I-SceI and determined that the distance between the complexes is 500 kb in a MAT-1 strain and 430 kb in a MAT-2 strain. Characterization of the organization of the known genes within the a and b gene complexes provided evidence for nonhomology and sequence inversion between MAT-1 and MAT-2. Antibiotic-resistance markers also were used to tag the a gene complex in MAT-1 strains (phleomycin) and the b gene complex in MAT-2 strains (hygromycin). Crosses were performed with these strains and progeny resistant to both antibiotics were recovered at a very low frequency, suggesting that recombination is suppressed within the MAT region. Overall, the chromosome homologues carrying the MAT locus of U. hordei share features with primitive sex chromosomes, with the added twist that the MAT locus also controls pathogenicity. (+info)
Molecular cloning and characterization of a cysteine-rich 16.6-kDa prolamin in rice seeds.
An alcohol-soluble storage protein, a 16.6-kDa prolamin found in rice seeds, was purified from both the total protein body and purified type I protein body fractions. The partial amino acid sequences of three tryptic peptides generated from the purified polypeptide were analyzed. A part of the 16.6-kDa prolamin cDNA was amplified from developing seed mRNA by the reverse transcribed polymerase chain reaction using an oligo (dT) primer and a primer which was synthesized based on the partial amino acid sequence. The amplified product was used to isolate the full-length cDNA clone (lambda RP16) from a developing seed cDNA library. The cDNA has an open reading frame encoding a hydrophobic polypeptide of 149 amino acids. The polypeptide was rich in glutamine (20.0%), cysteine (10.0%), and methionine (6.9%). The cysteine content was higher than those of most other rice storage proteins. Messenger RNA of the 16.6-kDa prolamin was detected in seeds, but not in other aerial tissues. (+info)