RNA Synthesis and Processing in Adenovirus-infected Cells

Animal DNA viruses provide a powerful system for analysis of transcription and translation in mammalian cells. During productive infection, ade-novirus DNA enters the nucleus rapidly (Lonberg-Holm and Philipson 1969) and is transcribed into large RNA molecules (Green t al. 1970; McGuire et al. 1972; Wall et al. 1972). Both early and late in productive infection, these RNA molecules be-come polyadenylated (Philipson et al. 1971) and cleaved (Parsons and Green 1971; Parsons et al. 1971; McGuire et al. 1972; Philipson et al. 1973) prior to entry into the cytoplasm. The switch from early to late gene xpression, which occurs at the onset of DNA synthesis, encompasses both a quanti-tative and a qualitative change with regard to the viral mRNA associated with the polyribosomes. Late in infection the cytoplasm contains about 10 times more viral RNA than early (Green et al. 1970; Philipson et al. 1973), and early and late mRNA is composed of different RNA size classes as shown by polyacrylamide gel electrophoresis (Parsons and Green 1971; Parsons et al. 1971; Lindberg et al. 1972). Host cell RNA synthesis is suppressed late in productive infection. Only 10-20 % of the normal amount of ribosomal RNA is transported tothe cyto-plasm (Raskas et al. 1970; Philipson et al. 1973), although significant amounts of the 45S precursor to ribosomal RNA is synthesized (Raskas et al. 1970; Ledinko 1972). Almost all messenger RNA which is transported to the cytoplasm late aider in-fection is viral (Lindberg et al. 1972), whereas the synthesis of host cell heterogeneous nuclear RNA (HnRNA) has been claimed to continue (Price and Penman 1972; McGuire et al. 1972). Sequences from both the complementary strands of adenovirus type 2 (Ad2) DNA are present in prep-arations of mRNA early as well as late in productive infection (Green et al. 1970; Landgraf-Leurs and Green 1973; Tibbetts et al. 1974). Early mRNA se-quences also seem to persist in the cytoplasm late after infection (Thomas and Green 1969; Green et