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 in Saccharomyces cerevisiae. Mutations in genes encoding the THO complex confer strong transcription-impairment and hyperrecombination phenotypes in the bacterial lacZ gene. 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 GAL1 promoter, we show that the negative effect of lacZ sequences on transcription depends on their distance from the promoter. In parallel, we show that transcription of either a long LYS2 fragment or the S. cerevisiae YAT1 G؉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.The control of genome stability is essential to ensure maintenance of genetic information in all cells of a living organism. Dysfunction of this control causes mutations and chromosomal aberrations that can give rise to loss of gene function, cell death, or irreversible changes in the cell program.Genetic recombination is required for mitotic DNA repair and for proper meiotic chromosome segregation. In addition, it may also be responsible for processes of genetic instability. A number of animal diseases, including cancer, originate by events of mitotic recombination between repeats that lead to chromosomal aberrations (34). Several elements have been described to enhance mitotic recombination, including DNA damage, replication defects, alteration of chromatin structure, and transcriptional activity (reviewed in reference 3). Ikeda and Matsumoto (26) first described the influence of transcription on recombination showing that recombination of phage was stimulated by transcription. In yeast, the first example of transcription-associated recombination was the finding that a hotspot of ribosomal DNA (rDNA) recombination, HOT1, was dependent on RNA polymerase I-driven transcription (55, 60). Thomas and Rothstein (56) extended transcription-induced recombination to sequences transcribed by RNA polymerase II (RNAPII). Additional examples of RNAPII-dependent recombination have been subsequently described in yeast (21,36,50) and mammalian cells (37, 57). Special mention must be made of the modulation of recombination at the immunoglobulin loci, as both V(D)J recombination (7, 31, 38) and class switching (15) are positively controlled by transcription.A gene linking transcription and genome instability in Saccharomyces cerevisae is HPR1, as hpr1 mutants show both increased l...

Relationship between G+C content, ORF‐length and mRNA concentration in Saccharomyces cerevisiae

“…On other grounds, there is experimental evidence that mRNA biogenesis of particular DNA segments in yeast may be modulated according to their length and G+C content (Chávez et al, 2001). This effect has been observed in hpr mutants which lack one of the components of THO, a heteromeric protein complex formed by Tho2, Hpr1, Mft1 and Thp2 (Prado et al, 1997;Chávez and Aguilera, 1997;Piruat and Aguilera, 1998;Chávez et al, 2000).…”

An allelic series for studying the mouse Thoc1 gene

“…Hpr1p genetically and physically interacts with RNA PolII (Chang et al, 1999;Chavez et al, 2000;Fan et al, 1996;Strasser et al, 2002). Hpr1p is an essential component of TREX since its loss impairs both transcriptional elongation and nuclear RNA export (Chavez and Aguilera, 1997;Chavez et al, 2001;Fan et al, 1996;Huertas and Aguilera, 2003;Rondon et al, 2003;Strasser et al, 2002;Zenklusen et al, 2002). Despite the defects in gene expression associated with HPR1 loss, it is not essential for yeast viability (Aguilera and Klein, 1990).…”

Activation-induced cytidine deaminase action is strongly stimulated by mutations of the THO complex

“…It is believed that THO controls the cotranscriptional formation of exportcompetent mRNP during transcription elongation by controlling the assembly of heterogeneous nuclear ribonucleoproteins onto the nascent mRNA (21). Hyperrecombination of THO mutants is particularly evident in long and GC-rich DNA sequences such as the bacterial lacZ gene (26). Because hyperrecombination depends on the formation of DNA:RNA hybrids (22), it has been proposed that one function of THO/TREX is to prevent the nascent mRNA from interacting with the template DNA to form R-loops.…”

“…It interacts with the Sub2 RNA-dependent ATPase and the Yra1 RNA-binding protein to form the TREX complex (23). THO has been shown to be required for the transcription of long genes and genes containing either high GC content or multiple internal repeats (25,26). It is believed that THO controls the cotranscriptional formation of exportcompetent mRNP during transcription elongation by controlling the assembly of heterogeneous nuclear ribonucleoproteins onto the nascent mRNA (21).…”