Transcription initiation by mammalian RNA polymerase II is effected by multiple common factors interacting through minimal promoter elements and regulated by gene-specific factors interacting with distal control elements. Minimal promoter elements that can function independently or together, depending on the specific promoter, include the upstream TATA box and a pyrimidine-rich initiator (Inr) overlapping the transcription start site. The binding of TFIID to the TATA element promotes the assembly of other factors into a preinitiation complex but factors which function at the Inr have not been defined. We show here that a novel factor (TFII-I) binds specifically to Inr elements, supports basal transcription from the adenovirus major late promoter and is immunologically related to the helix-loop-helix activator USF. We further show that TFII-I also binds to the upstream high-affinity USF site (E box), that USF also binds to the Inr, and that TFII-I and USF interact cooperatively at both Inr and E box sites. Thus, TFII-I represents a novel type of transcription initiation factor whose interactions at multiple promoter elements may aid novel communication mechanisms between upstream regulatory factors and the general transcriptional machinery.
RNA polymerase II is distinguished by its large carboxyl-terminal repeat domain (CTD), composed of repeats of the consensus heptapeptide Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7. Differential phosphorylation of serine-2 and serine-5 at the 5' and 3' regions of genes appears to coordinate the localization of transcription and RNA processing factors to the elongating polymerase complex. Using monoclonal antibodies, we reveal serine-7 phosphorylation on transcribed genes. This position does not appear to be phosphorylated in CTDs of less than 20 consensus repeats. The position of repeats where serine-7 is substituted influenced the appearance of distinct phosphorylated forms, suggesting functional differences between CTD regions. Our results indicate that restriction of serine-7 epitopes to the Linker-proximal region limits CTD phosphorylation patterns and is a requirement for optimal gene expression.
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