RNA POLYMERASE-II INITIATION-FACTOR INTERACTIONS AND TRANSCRIPTION START SITE SELECTION

An RNA polymerase II transcription system was resolved and reconstitut ed from extracts of Schizosaccharomyces pombe. Exchange with component s of a Saccharomyces cerevisiae visiae system was undertaken to reveal the factor or factors responsible for the difference in location of t he transcription start site, about 30 base pairs and 40 to 120 base pa irs downstream of the TATA box in S. pombe and S. cerevisiae, respecti vely. Two components, counterparts of human transcription factor IIF ( TFIIF) and TFIIH, could be exchanged individually between systems with out effect on the start site. Three components, counterparts of human TFIIB, TFIIE, and RNA polymerase II, could not be exchanged individual ly but Gould be swapped in the pairs TFIIE-TFIIH and TFIIB-RNA polymer ase II, which demonstrates that there are functional interactions betw een these components. Moreover, exchange of the latter pair shifted th e starting position, which shows that TFIIB and RNA polymerase II are solely responsible for determining the start site of transcription.