Regulation of the polyoma virus life cycle via A-to-I editing of overlapping poly(A) sites.

摘要

Mouse polyoma virus contains a small double stranded DNA genome with early and late gene transcribed from opposite strands. During the viral life cycle there is a striking transition between early and late phases gene expression. At early times, genes encoded from the early transcription unit are predominantly expressed. After the onset of viral DNA replication, expression of genes encoded from the late transcription unit increases dramatically, far exceeding that from the early strand. Previous work has suggested that the regulation is post-transcriptional in nature. At late times, primary late-strand transcripts are inefficiently polyadenylated, leading to the generation of long, multi-genomic RNAs that downregulate early-strand gene expression by inducing RNA editing. My thesis researches present evidence that the inefficiently of late RNA polyadenylation at late times may also be due to RNA editing. The poly(A) region of polyoma virus early-strand and late-strand RNA overlaps. RNAs in this overlapping region contain high level of inosines at late times in viral infection. RNAi knockdown of ADAR1 influences the early-late switch pattern. Furthermore, viruses that are otherwise identical, but have their early and late poly(A) signals separated so as to eliminate overlap, exhibit decreased poly(A) site read-through in their late-strand RNAs and lose their early-late switch. This effect is strongly dependent on the distance of separation between the two polyadenylation signals, but not the sequences between them. These and other results indicate that poly(A) region editing may underline the regulation of the polyoma virus life cycle, and it may represent a new form of gene regulation.