Hpr1 Is Preferentially Required for Transcription of Either Long or G+C-Rich DNA Sequences in Saccharomyces cerevisiae

Abstract

Hpr1 forms, together with Tho2, Mft1, and Thp2, the THO complex, which controls transcription elongation and genome stability inSaccharomyces cerevisiae. Mutations in genes encoding the THO complex confer strong transcription-impairment and hyperrecombination phenotypes in the bacterial lacZgene. In this work we demonstrate that Hpr1 is a factor required for transcription of long as well as G+C-rich DNA sequences. Using different lacZ segments fused to the GAL1promoter, we show that the negative effect of lacZsequences on transcription depends on their distance from the promoter. In parallel, we show that transcription of either a longLYS2 fragment or the S. cerevisiae YAT1G+C-rich open reading frame fused to the GAL1 promoter is severely impaired in hpr1 mutants, whereas transcription of LAC4, the Kluyveromyces lactis ortholog of lacZ but with a lower G+C content, is only slightly affected. The hyperrecombination behavior of the DNA sequences studied is consistent with the transcriptional defects observed in hpr1 cells. These results indicate that both length and G+C content are important elements influencing transcription in vivo. We discuss their relevance for the understanding of the functional role of Hpr1 and, by extension, the THO complex.