There is significant overlap between the 275 RHF genes and a set of 97 genes identified in a screen for host genes that affect the replication of BMV in yeast. Twenty genes were identified in both screens, including 14 genes whose absence inhibited BMV rep lication or expression and six genes who absence increased BMV replication or expression. This over lap could be a reflection of parallels http://www.selleckchem.com/products/INCB18424.html between BMV replication complex assembly and Ty1 VLP assembly. There are notable similarities between positive strand RNA virus replication and retroviral particle assembly, including recognition of discrete cis acting signals in the RNA genome by an element encoded protein and sequestration of the RNA in a nuclease resistant, membrane associated self assembling protein core.

Therefore, the finding that Ty1 and BMV utilize an overlapping set of host co factors may indi cate that there is more similarity in the cellular pro cesses that influence replication of positive sense RNA viruses, retroviruses and retrotransposons than might have been expected based on the differences in their structures and mechanisms of replication. Ribosome associated proteins were significantly enriched among RHFs. Many features of Ty1 RNA structure and function suggest that its translation may be an important regulatory step in retrotransposition. Ty1 RNA differs from typical cellular mRNAs in that it is partitioned between translation and packaging. Moreover, the 5,700 nucleotide Ty1 RNA is an unusually long RNA in yeast, and it encodes two ORFs, the second of which is expressed only when a programmed ribosomal frameshift occurs.

Third, the 5 end of Ty1 RNA, including the 53 nucleotide 5 UTR and the first 150 nucleotides of the gag ORF, is predicted to form an extended stem loop structure that is likely to play a repressive role in translation. Thus, ribosomal pro teins and ribosome biogenesis factors that function as RHFs could participate in the regulation of Ty1 RNA translation. However, our data suggest that a significant proportion of these RHFs do not influence Ty1 cDNA levels, and there fore are not likely to directly control Ty1 RNA translation. For example, deletions of genes encoding 60 S ribosomal subunit proteins Rpl33b, Rpl34a, and Rpl37a, 40 S subunit proteins Rps11a, Rps19a, and Rps27b, ribosome biogenesis factors Rsa3 and Utp30, and the ribosome associated chaperone, Zuo1 did not reduce Ty1 cDNA levels substan tially.

In addition, none of the RHFs that encode mitochon drial ribosome proteins had a significant effect on Ty1 cDNA levels. Deletion of RHFs that are required for Gag expression or translational frameshifting from gag to pol would be expected to reduce the level Batimastat of Ty1 cDNA, be cause the ratio of Gag to Gag Pol is critical for Ty1 pro tein processing, and processing, in turn, is required for cDNA synthesis.