Transcription terminates near the poly(A) site in the CYC1 gene of the yeast Saccharomyces cerevisiae.

A 38-base-pair region required for normal CYC1 mRNA 3' end formation in Saccharomyces cerevisiae was shown to be necessary for the termination of transcription in vivo by examining the stability of CEN3 plasmids. CEN3 plasmids were stably maintained during vegetative growth, unless a GAL1 transcript impinged on the CEN3 region. Transcription from the GAL1 promoter was terminated, and plasmid stability was restored by the insertion of a fragment containing the 38-base-pair region of CYC1. In contrast, a similar fragment lacking the 38-base-pair region had no such stabilizing effect. Furthermore, CYC1 mRNA transcription terminated in a region less than 100 nucleotides downstream from the normal poly(A) site, thus establishing that CYC1 mRNA 3' end formation does not involve overly extended precursors as are observed in higher eukaryotes.