Potato virus Y (PVY) the type member of the genus Potyvirus, occurs wodd-wide as isolates which differ in host range and the type of symptoms caused. The sequences of a 5' segment of viral RNA overlapping the 5' non-translated region (5'NTR) alone (ten isolates) or the 5'NTR and the adjacent P1 coding region (eight isolates) were established. These data were used to quantify the polymorphism in the Y-terminal part of the PVY genome. Nucleotide sequence identity between isolates ranged from 66-100 % in the 5'NTR and from 70-100% in the P1 coding region. The lowest amino acid sequence similarity between PVY P1 was 77%, illustrating the high variability of this protein in the PVY species. Phylogenetic trees based on either 5'NTR or P1
Three potato virus Y isolates, representatives of distinct PVY groups, identified in potato fields in northern Poland were submitted to biological and molecular analysis. Phenotypically, two isolates, PVYN-Ny and PVYN-Wi, belong to the necrotic strain and the third one (PVYO-LW) to the common strain. PVYN-Wi, however, did not react with monoclonal antibodies directed against the necrotic strain isolates which recognise PVYN-Ny. To characterise the isolates, coat protein genes were sequenced and compared with sequences from databases. The necrotic PVYN-Wi isolate showed 99% amino acid homology with the common one-PVYO-LW and significantly differed from the second necrotic isolate (PVYN-Ny). Sequence based homology matrix and phylogenetic analysis lead to classification of PVYN-Ny into group I, encompassing solely necrotic strain isolates, whereas PVYN-Wi falls into a phenotypically heterogeneous group II. The sequence analysis allowed for identification of putative group I-specific epitopes. 3'NTR (non-translated region) sequences were identical for PVYN-Wi and PVYO-LW. The 5'NTR, P1 gene, coat protein gene and 3'NTR sequences of the common (PVYO-LW) and the necrotic (PVYN-Wi) isolates are 99-100% homologous. This suggests that tobacco veinal necrosis determinants are located outside the 3' and 5' terminal sequences of the PVY genome.
Elongin C is a highly conserved, low molecular weight protein found in a variety of multiprotein complexes in human, rat, fly, worm, and yeast cells. Among the best characterized of these complexes is a mammalian E3 ligase that targets proteins for ubiquitination and subsequent degradation by the 26 S proteasome. Despite its crucial role as a component of such E3 ligases and other complexes, the specific function of Elongin C is unknown. In yeast, Elongin C is a non-essential gene and there is no obvious phenotype as associated with its absence. We previously reported that in Saccharomyces cerevisiae Elongin C (Elc1) interacts specifically and strongly with a class of proteins loosely defined as stress response proteins. In the present study, we examined the role of yeast Elc1 in the turnover of two of these binding partners, Snf4 and Pcl6. Deletion of Elc1 resulted in decreased steady-state levels of Snf4 and Pcl6 as indicated by Western blot analysis. Northern blot analysis of mRNA prepared from elc1 null and wild type strains revealed no difference in mRNA levels for Snf4 and Pcl6 establishing that the effects of Elc1 are not transcriptionally mediated. Reintroduction of either yeast or human Elongin C into Elc1 null strains abrogated this effect. Taken together, these data document that the levels of Snf4 and Pcl6 are dependent on the presence of Elc1 and that binding to Elc1 inhibits the degradation of these proteins. The results suggest a new function for yeast Elongin C that is distinct from a direct role in targeting proteins for ubiquitination and subsequent proteolysis.
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