Transcription of adenovirus 5 early region 1b is elevated in permissive cells infected by a mutant with an upstream deletion.
Early region 1b (E1b) of adenovirus 5 consists of a single transcription unit that lies from 1,702 to 4,070 nucleotides from the conventional left end of the genome. The effect of mutations that map upstream of E1b on the production of E1b mRNA was examined in vivo with mutants defective in gene functions from the neighboring early region 1a (E1a) transcription unit (499 to 1,632 nucleotides from the left end). These host range mutants replicate in the adenovirus 5-transformed human cell line 293. E1b mRNA accumulation was assayed by DNA-RNA hybridization late after productive infection when the E1b transcripts are abundant in the cytoplasm. Cells infected by wild-type virus, mutant dl311, or mutant hr1. The elevated levels of E1b mRNA were also detected in steady-state nuclear RNA, pulse-labeled polyadenylated nuclear RNA, and pulse-labeled total nuclear RNA. These data indicate that E1b transcription was elevated in human 293 cells infected with dl312. There was no evidence of increases in genomic DNA in dl312-infected cells, suggesting that the rate of transcription may be elevated. When mixed infections with a 10-fold excess of either dl312 or wild-type virus were performed, the phenotype was that of the more abundant genome. This result suggests that the respective phenotypes were cis dominant. The increased rate of transcription can be attributed to cis-active regulatory effects of the deletion of nucleotides 448 to 1,349 in mutant dl312 DNA.