THO complex subunit 1 (THOC1; its homologues from plants and yeast HPR1) is a component of the THO subcomplex of the TREX complex, which is involved in coupling mRNA transcription, processing and nuclear export, and specifically associates with spliced mRNA and not with unspliced pre-mRNA. TREX plays central roles during mRNP (messenger ribonucleoprotein) maturation and export from the nucleus to the cytoplasm []. The THO complex is recruited to transcribed genes and moves along the gene with the elongating polymerase during transcription. THO is important for stabilizing nascent RNA in the RNA polymerase II elongation complex by preventing formation of DNA:RNA hybrids behind the elongating polymerase [, , ]. In plants, HPR1 plays a role in disease resistance [].
The THO/TREX complex is the transcription- and export-related complex associated with spliceosomes that preferentially deal with spliced mRNAs as opposed to unspliced mRNAs. Thoc2 plays a role in RNA polymerase II (RNA pol II)-dependent transcription and is required for the stability of DNA repeats []. In humans, the TRE complex is comprised of the exon-junction-associated proteins Aly/REF and UAP56 together with the THO proteins THOC1 (hHpr1/p84), Thoc2 (hRlr1), THOC3 (hTex1), THOC5 (fSAP79), THOC6 (fSAP35), and THOC7 (fSAP24). Although much evidence indicates that the function of the TREX complex as an adaptor between the mRNA and components of the export machinery is conserved among eukaryotes, in Drosophila the majority of mRNAs can be exported from the nucleus independently of the THO complex []. This entry represents a conserved domain found towards the N terminus of these proteins.
