Initiation by RNA polymerase II and formation of runoff transcripts containing unblocked and unmethylated 5' termini

Transcription of cloned adenovirus, beta-globin, and retrovirus long terminal repeat DNAs in HeLa whole-cell lysate was inhibited by S-adenosylhomocysteine. However, full-length 1.7-kilobase transcripts made on adenovirus 2 late promoter DNA contained 5'-terminal GpppA, consistent with specific initiation and runoff synthesis in the absence of product methylation. Formation of runoff transcripts including retrovirus RNAs that normally contain 5'-m7GpppGmpC was not decreased by replacing GTP with non-hydrolyzable analogs, and Rous-associated virus-2 runoff products made in the presence of GTP-gamma-S contained 5'-terminal gamma-S-pppGpC. The results indicate that capping and specific transcript synthesis by RNA polymerase II are not obligatorily linked in HeLa whole-cell lysate. Accurate initiation is dependent on ATP hydrolysis, and in contrast to GTP, replacement of ATP by 5'-adenylyl-imidodiphosphate blocked specific initiation of transcripts that start with either GTP (Rous-associated virus-2, Rous-associated virus-0) or ATP (beta-globin, adenovirus).