A general transcription factor forms a stable complex with RNA polymerase B (II).

A general transcription factor (BTF3) has been purified from HeLa whole cell extracts and shown to be required for accurate initiation of transcription from the adenovirus-2 major late promoter (Ad2MLP) and other RNA polymerase class B promoters. We show that purified BTF3 (27 kd) binds to RNA polymerase B (II), forming a complex that is transcriptionally active. We found no evidence that purified BTF3 interacts with DNA or is required for the formation of the stable preinitiation complex.