1. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
2. Banting and Best Department of Medical Research, University of Toronto, 112 College Street, Toronto, Ontario, Canada M5G 1L6
3. Bauer Center for Genomics Research, Harvard University, 7 Divinity Ave., Cambridge, Massachusetts 02138, USA

Correspondence to: Stephen Buratowski¹ Email: steveb@hms.harvard.edu

Abstract

The carboxy-terminal domain (CTD) of the RNA polymerase II (RNApII) largest subunit consists of multiple heptapeptide repeats with the consensus sequence YSPTSPS. Different CTD phosphorylation patterns act as recognition sites for the binding of various messenger RNA processing factors, thereby coupling transcription and mRNA processing¹. Polyadenylation factors are co-transcriptionally recruited by phosphorylation of CTD serine 2 (ref. 2) and these factors are also required for transcription termination^{3, 4}. RNApII transcribes past the poly(A) site, the RNA is cleaved by the polyadenylation machinery, and the RNA downstream of the cleavage site is degraded. Here we show that Rtt103 and the Rat1/Rai1 5' 3' exonuclease are localized at 3' ends of protein coding genes. In rat1-1 or rai1 cells, RNA 3' to polyadenylation sites is greatly stabilized and termination defects are seen at many genes. These findings support a model in which poly(A) site cleavage and subsequent degradation of the 3'-downstream RNA by Rat1 trigger transcription termination^{5, 6}.

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