Kinetics of ribosomal pausing during programmed -1 translational frameshifting.
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In the Saccharomyces cerevisiae double-stranded RNA virus, programmed -1 ribosomal frameshifting is responsible for translation of the second open reading frame of the essential viral RNA. A typical slippery site and downstream pseudoknot are necessary for this frameshifting event, and previous work has demonstrated that ribosomes pause over the slippery site. The translational intermediate associated with a ribosome paused at this position is detected, and, using in vitro translation and quantitative heelprinting, the rates of synthesis, the ribosomal pause time, the proportion of ribosomes paused at the slippery site, and the fraction of paused ribosomes that frameshift are estimated. About 10% of ribosomes pause at the slippery site in vitro, and some 60% of these continue in the -1 frame. Ribosomes that continue in the -1 frame pause about 10 times longer than it takes to complete a peptide bond in vitro. Altering the rate of translational initiation alters the rate of frameshifting in vivo. Our in vitro and in vivo experiments can best be interpreted to mean that there are three methods by which ribosomes pass the frameshift site, only one of which results in frameshifting. (+info)
Purification and characterization of infectious myonecrosis virus of penaeid shrimp.
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The causative agent of myonecrosis affecting cultured Penaeus vannamei in Brazil was demonstrated to be a virus after purification of the agent from infected shrimp tissues. Purified viral particles were injected into specific pathogen-free P. vannamei, resulting in a disease that displayed the same characteristics as those found in the original shrimp used for purification. The virus was named infectious myonecrosis virus (IMNV). The viral particles were icosahedral in shape and 40 nm in diameter, with a buoyant density of 1.366 g ml(-1) in caesium chloride. The genome consisted of a single, double-stranded (dsRNA) molecule of 7560 bp. Sequencing of the viral genome revealed two non-overlapping open reading frames (ORFs). The 5' ORF (ORF 1, nt 136-4953) encoded a putative RNA-binding protein and a capsid protein. The coding region of the RNA-binding protein was located in the first half of ORF 1 and contained a dsRNA-binding motif in the first 60 aa. The second half of ORF 1 encoded a capsid protein, as determined by amino acid sequencing, with a molecular mass of 106 kDa. The 3' ORF (ORF 2, nt 5241-7451) encoded a putative RNA-dependent RNA polymerase (RdRp) with motifs characteristic of totiviruses. Phylogenetic analysis based on the RdRp clustered IMNV with Giardia lamblia virus, a member of the family Totiviridae. Based on these findings, IMNV may be a unique member of the Totiviridae or may represent a new dsRNA virus family that infects invertebrate hosts. (+info)
Molecular characterization of the largest mycoviral-like double-stranded RNAs associated with Amasya cherry disease, a disease of presumed fungal aetiology.
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The sequence of the four large (L) double-stranded RNAs (dsRNAs) associated with Amasya cherry disease (ACD), which has a presumed fungal aetiology, is reported. ACD L dsRNAs 1 (5121 bp) and 2 (5047 bp) potentially encode proteins of 1628 and 1620 aa, respectively, that are 37% identical and of unknown function. ACD L dsRNAs 3 (4458 bp) and 4 (4303 bp) potentially encode proteins that are 68% identical and contain the eight motifs conserved in RNA-dependent RNA polymerases (RdRp) of dsRNA mycoviruses, having highest similarity with those of members of the family Totiviridae. Both terminal regions share extensive conservation in all four RNAs, suggesting a functional relationship between them. As ACD L dsRNAs 1 and 2 do not encode RdRps, both are probably replicated by those from either ACD L dsRNA 3 or 4. Partial characterization of the equivalent L dsRNAs 3 and 4 associated with cherry chlorotic rusty spot revealed essentially identical sequences. (+info)
'2A-like' and 'shifty heptamer' motifs in penaeid shrimp infectious myonecrosis virus, a monosegmented double-stranded RNA virus.
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Penaeid shrimp infectious myonecrosis virus (IMNV) is a monosegmented double-stranded RNA virus that forms icosahedral virions and is tentatively assigned to the family Totiviridae. New examinations of the IMNV genome sequence revealed features not noted in the original report. These features include (i) two encoded '2A-like' motifs, which are likely involved in open reading frame (ORF) 1 polyprotein 'cleavage'; (ii) a 199 nt overlap between the end of ORF1 in frame 1 and the start of ORF2 in frame 3; and (iii) a 'shifty heptamer' motif and predicted RNA pseudoknot in the region of ORF1-ORF2 overlap, which probably allow ORF2 to be translated as a fusion with ORF1 by -1 ribosomal frameshifting. Features (ii) and (iii) bring the predicted ORF2 coding strategy of IMNV more in line with that of its closest phylogenetic relative, Giardia lamblia virus, as well as with that of several other members of the family Totiviridae including Saccharomyces cerevisiae virus L-A. (+info)