Specific transcription from the adenovirus E2E promoter by RNA polymerase III requires a subpopulation of TFIID.

The early E2 (E2E) promoter of adenovirus type 2 possesses a TATA-like element and binding sites for the factors E2F and ATF. This promoter is transcribed by RNA polymerase II in high salt nuclear extracts, but by RNA polymerase III in standard nuclear extracts, as judged by sensitivity to low and high, respectively, concentrations of alpha-amanitin. Transcription by the two RNA polymerases initiated at the same site and depended, in both cases, on the TATA-like sequence and upstream elements. However, RNA polymerase III transcripts, unlike those synthesized by RNA polymerase II, terminated at two runs of Ts downstream of the initiation site. Although they are not essential, sequences downstream of the initiation site increased the efficiency of E2E transcription by RNA polymerase III. Such RNA polymerase III dependent transcription required a subpopulation of the general transcription factor, TFIID: TFIID that binds weakly to phosphocellulose (0.3 M eluate) complemented a TFIID-depleted extract to restore RNAp III transcription, whereas TFIID tightly associated with phosphocellulose (1 M eluate) was unable to do so.