Genes with internal repeats require the THO complex for transcription

Abstract

The evolutionarily conserved multisubunit THO complex, which is recruited to actively transcribed genes, is required for the efficient expression of FLO11 and other yeast genes that have long internal tandem repeats. FLO11 transcription elongation in Tho ؊ mutants is hindered in the region of the tandem repeats, resulting in a loss of function. Moreover, the repeats become genetically unstable in Tho ؊ mutants. A FLO11 gene without the tandem repeats is transcribed equally well in Tho ؉ or Tho ؊ strains. The Tho ؊ defect in transcription is suppressed by overexpression of topoisomerase I, suggesting that the THO complex functions to rectify aberrant structures that arise during transcription.T ranscription involves a highly orchestrated series of events in which the core polymerase is joined by many additional proteins that promote initiation, elongation, and termination (1-3). Efficient transcription also depends on the configuration of the DNA template because transcription creates negative supercoils behind the polymerase and positive supercoils ahead of it (4-6). These alterations in the superhelical density could permit repetitive sequences to form structures that impede the progress of the polymerase and promote recombination. For example, excessive supercoiling in yeast leads to hyperrecombination at the highly repetitive rRNA-encoding DNA locus (7,8). The DNA landscape may therefore influence the efficiency of transcription, and some of the elongation factors could be required to remodel the template to permit efficient transcription.The Saccharomyces cerevisiae multisubunit THO complex, which has been identified as a possible elongation component, has been associated with many aspects of RNA and DNA metabolism (9-12). The complex consists of four tightly bound proteins (Hpr1, Tho2, Thp1, and Mft1) (13), two of which (Hpr1 and Tho2) are conserved from yeast to humans (14). Biochemical studies using natural templates have implicated the THO complex in recruiting the mRNA export proteins Sub2 (UAP56 in humans) and Yra1 (Aly1) to the mRNA in both yeast (15) and humans (14). In yeast, ChIP immunoprecipitation experiments indicate that the THO complex is recruited to actively transcribed genes (16)(17)(18).The biochemical analysis of the function of the THO complex has not led to a consistent picture. Experiments using a GAL1 promoted Escherichia coli lacZ reporter construct expressed in yeast suggested that transcription elongation of the lacZ gene is reduced in an hpr1⌬ mutant (19). Further analysis using a P GAL -lacZ system indicated that in a Tho Ϫ mutant DNA:RNA hybrids are formed in vivo between the nascent transcript and the DNA template (20). Because the transcription of GC-rich lacZ constructs was THO-dependent, whereas that of many endogenous yeast genes was not, it was proposed that the THO complex is required for efficient transcription elongation of long and GC-rich genes (21). Moreover, the role of the THO complex in elongation has been questioned based on the insensitivity of Tho Ϫ mutants to ...

Identification of mRNAs that are spliced but not exported to the cytoplasm in the absence of THOC5 in mouse embryo fibroblasts

“…In agreement with these data, THOC1 depletion does not influence the expression of Hsp70 under the non-heat-shock condition in several human cancer cell lines (Li et al 2007). Similarly, it has been discussed in the yeast system that some genes, such as TIR1 (Voynov et al 2006), may require the THO complex upon induction or some environmental stress condition that requires enhanced transcription. Furthermore, since Hsp70 mRNA was isolated from the THOC5 complex at 42°C but not at 37°C, genes whose transcription creates aberrant structures under stress conditions could also require the THO complex.…”

“…The selection is not based on a common feature, such as homological domain (or motif) among the 10 mRNAs that have been identified here as THOC5-dependent mRNAs. In the yeast system, several motifs such as ''GC-rich'' or ''internal repeats'' were suggested as criteria for the THO complex dependency (Chavez et al 2001;Voynov et al 2006). In those reports, the THO complex is required for efficient transcription of genes with long tandem repeats upon induction or under some conditions, such as under stress and/or upon signaling-induced conditions.…”

Splicing-independent loading of TREX on nascent RNA is required for efficient expression of dual-strand piRNA clusters in Drosophila

“…In yeast, the THO/TREX complex participates in transcription, pre-mRNA processing, and nuclear mRNA export of the majority of genes. Yeast TREX associates with transcribing RNA polymerase II (Pol II) and is necessary for transcription elongation (Chavez et al 2001;Voynov et al 2006). TREX is loaded onto nascent transcripts during transcription (Lei et al 2001;Strasser et al 2002;Abruzzi et al 2004) and is essential for mRNA export from the nucleus, as the Yra1 subunit of TREX recruits the Mex67p protein, which interacts with nucleoporins and mediates passage of complexes of mRNAs and proteins (mRNPs) through the nuclear pore (Strasser and Hurt 2000;Stutz et al 2000).…”

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

“…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).…”