Transcription elongation through DNA arrest sites - A multistep process involving both RNA polymerase II subunit RPB9 and TFIIS

The role of yeast RNA polymerase II (pol II) subunit RPB9 in transcript elongation was investigated by examining the biochemical properties of pol II lacking RPB9 (pol II Delta 9). The maximal rate of chain elongation was nearly identical for pol II and pol II Delta 9. By contrast, pol II Delta 9 elongated more efficiently through DNA sequences that signal the elongation complex to pause or arrest. The addition of purified recombinant RPB9 to pol II Delta 9 restored the elongation properties of the mutant polymerase to those of the wild-type enzyme. Arrested pol II Delta 9 complexes were refractory to levels of TFIIS that promoted maximal read-through with pol II. However, both pol II and pol II Delta 9 complexes stimulated with TFIIS undergo transcript cleavage, confirming that transcript cleavage and read-through activities can be uncoupled. Our observations suggest that both TFIIS and RPB9 are required to stimulate the release of RNA polymerase II from the arrested state.