Ultraviolet transcriptional unit mapping for the late genes in adenovirus type 2
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At late times during the infection of human KB cells with Adenovirus type 2 (Ad 2), the ultraviolet (uv) sensitivity of transcription was assayed by DNA-RNA hybridization across the length of the genome. Assuming that the majority of the nuclear transcripts at this time of infection are read from the rightward transcribing DNA strand, the resulting plot of the surviving fraction of viral transcription vs. genome position indicates two transcription units are responsible for the transcription from selected DNA restriction fragments of the genome were also obtained. The uv inactivation cross sections generated from such curves identified a long, uv sensitive transcript originating from the major late promoter at approximately 17 map units, and a shorter, less uv sensitive from approximately 63 map units on the genome. The shorter transcription unit accounts for about one third to a half of the viral nuclear RNA synthesized from the right hand 30 to 40% of the genome. The majority of the late viral nuclear transcripts, however, originated at approximately 17 map units and terminated at around 60-70 map units. Similar experiments examining the uv sensitivity of cytoplasmic poly A RNA production at various sites across the length of the genome are consistent with two rightward transcribing transcription units expressed during late Ad 2 infection. The transcriptional organization of late Ad 2 gene expression was also approached through uv transcription unit mapping experiments by examining the uv sensitivities of the synthesis of late Ad 2 proteins for which the approximate gene locations are known. The effect of uv on Ad 2 nuclear transcription was also reflected at the polypeptide level indicating two transcription units are responsible for the synthesis of mRNA coding for late viral proteins. The differential radiosensitivities of late protein synthesis confirmed the relative gene positions on the Ad 2 genome.
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