The 8-nucleotide-long RNA:DNA hybrid is a primary stability determinant of the RNA polymerase II elongation complex

Abstract

The sliding clamp model of transcription processivity, based on extensive studies of Escherichia coli RNA polymerase, suggests that formation of a stable elongation complex requires two distinct nucleic acid components: an 8-9-nt transcript-template hybrid, and a DNA duplex immediately downstream from the hybrid. Here, we address the minimal composition of the processive elongation complex in the eukaryotes by developing a method for promoter-independent assembly of functional elongation complex of S. cerevisiae RNA polymerase II from synthetic DNA and RNA oligonucleotides. We show that only one of the nucleic acid components, the 8-nt RNA:DNA hybrid, is necessary for the formation of a stable elongation complex with RNA polymerase II. The double-strand DNA upstream and downstream of the hybrid does not affect stability of the elongation complex. This finding reveals a significant difference in processivity determinants of RNA polymerase II and E. coli RNA polymerase. In addition, using the imperfect RNA:DNA hybrid disturbed by the mismatches in the RNA, we show that nontemplate DNA strand may reduce the elongation complex stability via the reduction of the RNA:DNA hybrid length. The structure of a "minimal stable" elongation complex suggests a key role of the RNA:DNA hybrid in RNA polymerase II processivity.