Identification of a 3′ → 5′ exonuclease activity associated with human RNA polymerase II

Abstract

Human RNA polymerase II is shown to be associated with a 3′ → 5′ exonuclease activity that removes nucleoside 5′-monophosphates from the 3′ end of the transcripts in isolated ternary complexes. This activity is stimulated by SII, a protein that acts as a transcription elongation factor in vitro. In addition, we show that another transcription factor, TFIIF, stimulates a competing pyrophosphorolysis reaction. These findings raise interesting questions about the roles of these activities in vivo, including the possibility that this RNA polymerase may proofread the nascent transcript.