Separated strands of restriction endonuclease Eco R1 and Hpa 1 fragments of 32P-labeled Adenovirus 5 DNA have been used in saturation hybridization experiments with cytoplasmic RNA extracted from human cells infected with Adenovirus type 5. The results of such experiments have allowed the construction of maps of the regions of the viral genome complementary to both "early" and "late" Adenovirus 5 RNA. At early times during the lytic cycle, about 25% of the viral genome is expressed as mRNA. Adenovirus 5 DNA sequences complementary to "early" mRNA comprise four discrete regions, two on each strand, of the viral genome: except in one instance, these correspond to the regions of the Adenovirus 2 genome complementary to "early" Adenovirus 2 mRNA. In the exceptional case, "early" Adenovirus 5 mRNA appears to contain not only sequences corresponding, at least in position, to those expressed in Adenovirus 2-infected cells, but also some additional, adjacent sequences, reminiscent of the situation in human cells infected with the Adenovirus 2/Simian virus 40 hybrid viruses, Ad2+ND1 and Ad2+ND3 (Flint et al., 1975a). All, or almost all, the information encoded by the Adenovirus 5 genome is expressed as mRNA during the lytic cycle and most of the exclusively "late" mRNA is complementary to the r strand of Adenovirus 5 DNA. The separated strands of fragments of 32P-labeled Adenovirus 2 DNA generated by the restriction endonuclease Bam Hl have been used to improve the resolution of maps of both Adenovirus 2 and Adenovirus 5 "late" mRNA, which are described here.
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