Histones H3 and H4 are components of upstream activation factor required for the high-level transcription of yeast rDNA by RNA polymerase I

摘要

RNA polymerase I (Pol I) transcription in the yeast Saccharomyces cerevisiae is greatly stimulated in vivo and in vitro by the multiprotein complex, upstream activation factor (UAF). UAF binds tightly to the upstream element of the rDNA promoter, such that once bound (in vitro), UAF does not readily exchange onto a competing template. Of the polypep- tides previously identified in purified UAF, three are encoded by genes required for Pol I transcription in vivo: RRN5, RRN9, and RRN10. Two others, p30 and p18, have remained unchar- acterized. We report here that the N-terminal amino acid sequence, its mobility in gel electrophoresis, and the immu- noreactivity of p18 shows that it is histone H3.