Adjacent pol II and pol III promoters: transcription of the yeast retrotransposon Ty3 and a target tRNA gene

摘要

The Saccharomyces cerevlslae retrotransposon Ty3 Integrates 16 to 19 basepairs upstream of tRNA genes in a region where sequences have been shown to affect the expression of tRNA genes in vlvo and in vitro. Slgma, the isolated long terminal repeat of Ty3, is also found in this region. The purpose of these experiments was to elucidate the effects of Ty3 and sigma expression on that of an associated SUP2 tRNATyr gene In vivo. SUP2 pre-tRNA levels were moderately increased when SUP2 was associated with Ty3 or sigma in either orientation. These increases were independent of Ty3 or sigma promoter activity. The presence of Ty3 or sigma also increased the usage of a minor SUP2 transcription initiation site 2 basepalrs upstream of the major initiation site and within the 5 basepair direct repeat flanking Ty3 and sigma. Transcription from an isolated sigma directed toward the tRNA gene was observed to extend through the tRNA gene. In contrast to the lack of an effect of sigma induction on pre-tRNATyr levels, levels of this sigma transcilpt were Increased when the SUP2 promoter was inactivated by a single basepair mutation.