Transcription of adenovirus RNA polymerase III genes.

Abstract

Eukaryotic RNA polymerase (RNAp) III is responsible for synthesis of abundant, low molecular mass RNA species, including tRNA, 5S rRNA, and U6 snRNA (see Roeder 1976; Geiduschek and Tocchini-Valentini 1988). Although they are noncoding, RNAp III transcripts participate in such essential processes as translation, RNA processing, and protein targeting (see Rich and Raj Bhandary 1976; Guthrie and Patterson 1988; Dreyfuss et al. 1988; Steitz et al. 1988; Wolin and Walter 1991; Young 1991). Transcription of a viral genome by RNAp III was first recognized 20 years ago, when it was established that a small RNA specific to adenovirus-infected cells, virus-associated (VA) RNA (Reich et al. 1966), is synthesized by this enzyme. All adenovirus genomes examined to date encode at least one VA RNA species. Investigation of the organization of the transcriptional control regions of these viral RNAp III genes made an important contribution to the unexpected discovery of the intragenic location of elements of RNAp III promoters. As discussed in this review, the VA RNA I promoter of subgroup C adenoviruses, which is exceptionally active in in vitro systems, has provided an important model for investigation of the mechanism of initiation of transcription by this RNA polymerase. Elucidation of the part played by VA RNA I during adenovirus infection has, moreover, identified a previously unknown mechanism by which viruses can evade cellular defence systems.