A NOVEL RNA-POLYMERASE-I-DEPENDENT RNASE ACTIVITY THAT SHORTENS NASCENT TRANSCRIPTS FROM THE 3'-END

A novel RNase activity was identified in a yeast RNA polymerase I (pol I) in vitro transcription system. Transcript cleavage occurred at the 3' end and was dependent on the presence of ternary pol I/DNA/RNA com plexes and an additional protein factor not identical to transcription factor IIS (TFIIS). Transcript cleavage was observed both on arrested complexes at the linearized ends of the transcribed DNA and an intrin sic blocks of the DNA template. Shortened transcripts that remained as sociated within the ternary complexes were capable of resuming RNA cha in elongation. Passible functions of the nuclease for transcript elong ation or termination are discussed.