The mechanism of viral carcinogenesis by DNA mammalian viruses. VI. A new class of virus-specific RNA molecules in cells transformed by group C human adenoviruses

Hybridization of mRNA from adenovirus-transformed cells to segments of the adenovirus genome

Cytoplasmic viral-specific RNA from the 8617 line of adenovirus type 2 (Ad2) transformed rat cells was hybridized to DNA fragments derived either by Eco-RI or Sma-I restriction endonucleases. Three discrete classes of viral RNA (26S, 20S, and 15S) were detected by hybridization of total cytoplasmic RNA with the fragment, and all of these RNA molecules also hybridized to the much smaller Sma-E fragment of Ad2 DNA. Poly (A)-containing RNA (exposed to 90% formamide) contained only the 20S and 15S mRNA species, suggesting that the 26S RNA might be an aggregated species. Viral RNA of the same size derived from the same regions of the genome has not been detected in lytically infected cells, suggesting some change in the pattern of transcription or RNA processing of the Ad2 DNA in the integrated state.

Differential accumulation of virus-specific RNA during the cell cycle of adenovirus-transformed rat embyro cells

In adenovirus type 2-transformed rat embryo cells there is a threefold greater incorporation of [3-H]uridine into virus-specific RNA early in S phase than in late S or G2. This heightened accumulation of labeled RNA is true for both nuclear and cytoplasmic virus-specific labeling. Inhibition of DNA synthesis decreases the virus-specific RNA labeling, whereas reversal of inhibition again allows the elevated level of virus-specific RNA labeling.

Production of viral mRNA in adenovirus- transformed cells by the post- transcriptional processing of heterogeneous nuclear RNA containing viral and cell sequences

Adenovirus 2-transformed cells contain virus-specific sequences which are covalently linked to cell-specific RNA sequences in heterogeneous nuclear RNA (HnRNA) molecules larger than 45S. Virus sequences are identified by hybridization to viral DNA, and the cell sequences are detected by hybridization to cellular DNA under conditions where hybridization only occurs to reiterated sites in cell DNA. Such large composite viral-cell HnRNA molecules presumably arise through the uninterrupted transcription of host sequences and integrated viral DNA. Adenovirus-specific polysomal RNA from these cells sediments as three discrete species at 16, 20, and 26S. These specific classes of viral mRNA do not contain rapidly hybridizing host-specific RNA sequences. Both virus-specific HnRNA and mRNA contain polyadenylic acid sequences since they bind to polyU columns at levels characteristics of other polyA-terminated HnRNA and mRNA. Thus, the discrete species of virus-specific mRNA in adenovirus 2 transformed cells appear to be derived from high-molecular-weight virus-specific HnRNA through a series of post-transcriptional modifications involving polyA addition. Subsequently the HnRNA is cleaved so that the cell-specific RNA sequences that originate from the reiterated sites in cell DNA do not accompany the adenovirus mRNA to the cytoplasm. These events for the adenovirus-specific mRNA appear, therefore, to be similar to the stages in the biogenesis of the majority of mRNA in eukaryotic cells.

Virus-specific ribonucleic acid in the nucleus and cytoplasm of rat embryo cells transformed by adenovirus type 2

Nuclei were isolated from rat embryo cells transformed by adenovirus type 2. Nuclear and cytoplasmic virus-specific ribonucleic acids (RNA) were characterized and quantitated by deoxyribonucleic acid (DNA)-RNA hybrid formation with adenovirus DNA. The results indicate that most, if not all, virus-specific RNA molecules are synthesized in the cell nucleus and subsequently transported into cytoplasm where they degrade with a half-life of 1 to 2 hr. No difference in base sequences between nuclear and cytoplasmic virus-specific RNA species can be detected by hybridization competition experiment with viral DNA.

The mechanism of viral carcinogenesis by DNA mammalian viruses: RNA transcripts containing viral and highly reiterated cellular base sequences in adenovirus-transformed cells (DNA-RNA hybridization-viral-cell mRNA)

Virus-specific RNA was isolated from cells transformed by human adenovirus 2 and 7 by multiple hybridizations with and elutions from homologous viral DNA; RNA molecules purified by this selection procedure hybridized efficiently with both viral DNA (24-50%) and DNA from untransformed cells (12-27%). Virus-specific RNA isolated in the same manner from cells productively infected with adenoviruses did not hybridize significantly with cellular DNA. These findings suggest that RNA molecules containing covalently-linked viral and cellular sequences are transcribed in cells transformed by human adenoviruses. The high efficiency of hybridization with DNA from untransformed cells implies that viral DNA is integrated adjacent to highly reiterated cellular DNA sequences.

Mechanism of viral carcinogenesis by DNA mammalian viruses. VII. Viral genes transcribed in adenovirus type 2 infected and transformed cells

DNA-RNA hybridization-competition experiments were used to compare the virus-specific RNA sequences synthesized during productive infection with human adenovirus type 2 with those synthesized in virus-free adenovirus type 2 transformed cells. The "early" virus-specific RNA present at six hours after infection, prior to the onset of viral DNA synthesis, represents 8-20 percent (2 to 10 genes) of the viral genome. All viral RNA sequences synthesized early are also present "late," at 18 hours after infection. The base sequences transcribed in transformed cells are homologous to approximately 50 per cent of the sequences transcribed early after infection. Thus only 4 to 10 per cent of the viral genome, representing 1 to 5 viral genes, are transcribed in adenovirus type 2 transformed cells. The virus-specific RNA synthesized 18 hours after infection was not found in transformed cells, suggesting that either these late viral genes are not present or are not transcribed in adenovirus type 2 transformed cells.