The major late promoter of adenovirus-2 is accurately transcribed by RNA polymerases IIO, IIA, and IIB.

Subunit IIa of mammalian RNA polymerase II contains at its C terminus 52 tandem repeats of the consensus sequence Tyr-Ser-Pro-Thr-Ser-Pro-Ser. This domain is unmodified in RNA polymerase IIA, extensively phosphorylated in RNA polymerase IIO, and absent from RNA polymerase IIB. In an effort to define the role of the C-terminal domain, we have measured the transcriptional activity of purified RNA polymerases IIO, IIA, and IIB. The ability of each polymerase subspecies to transcribe the major late promoter of adenovirus-2 was examined in a polymerase-dependent transcription system reconstituted from partially purified transcription factors. RNA polymerases IIO, IIA, and IIB are all capable of initiating specific transcripts from this promoter. The transcriptional activity was determined as a function of the concentration of RNA polymerase II, template DNA, and each of the essential general transcription factors. The transcriptional activities of RNA polymerases IIA and IIB were comparable and consistently greater than that of RNA polymerase IIO when assayed under the conditions described here. The kinetics of transcript formation is similar except that RNA polymerase IIO has a more pronounced lag. These results show that the C-terminal domain of subunit IIa is not essential for the accurate initiation of transcripts from the major late promoter of adenovirus-2 and that the effect of the C-terminal domain is not likely mediated by the general transcription factors required for the expression of class II genes.