From the present experiments, we can conclude that late in infection two classes of DNA-dependent RNA polymerase transcribe the viral genome. Although we cannot definitively exclude the possibility that one or both of these enzymes are coded for by the virus, it appears more probable that these are hos enzymes, because of the coincidence of the alpha-amanitin sensitivities for synthesis of specific viral RNAs with the toxin sensitivities of the respective host RNA polymerases. Furthermore, the chromatographic properties of the enzymes, the alpha-amanitin sensitivities of the purified RNA polymerases and the levels of solubilized activities are the same for uninfected and late infected cells. It seems probable that some virus-coded or virus-induced factor(s) modifies either the selectivity or the activity of these host RNA polymerases. As an example, the "inactivation" of RNA polymerase I activity in vivo or the increased endogenous activity of isolated infected cell nuclei, without changes in the solubilized level of the respective RNA polymerases, could be mediated by such factor(s). The effect of such factors may not be detected by activity measurements on exogenous DNA, because it acts as a nonspecific template. Analysis of such factors will require reconstitution of appropriate in vitro systems, which retain some transcriptional specificity. Since several viral mRNAs synthesized at late times (Tal et al. 1974) and the 5.5S RNA (J. Pan, pers, comm.) are transcribed from the same region (R-R1 restriction enzyme fragment A), initiation and termination signals for both RNA polymerase II and III are contained in this portion of the genome. Further studies of the interaction of these two enzymes with the adenovirus 2 genome should contribute to understanding the control of transcription in eukaryotic cells, in particular in the case of virus-infected or -transformed cells.
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Weinmann et al. (1974) studied this question.