THOC1 is a protein that acts as component of the THO subcomplex of the TREX complex which is thought to couple mRNA transcription, processing and nuclear export, and which specifically associates with spliced mRNA and not with unspliced pre-mRNA. THOC1 is required for efficient export of polyadenylated RNA and it regulates transcriptional elongation of a subset of genes. The TREX complex is essential for the export of Kaposi's sarcoma-associated herpesvirus (KSHV) intronless mRNAs and infectious virus production. THOC1 is also involved in genome stability and participates in a TP53-independent apoptotic pathway via CASP6. THOC1 may be a useful biomarker for breast cancer diagnosis, as while it has low levels of expression in normal epithelial cells in the breast, it can be highly expressed in breast tumors. Degree of expression also correlates with tumor size, metastatic state and an aggressive phenotype of breast cancer. In immunohistochemistry of normal tissue, THOC1 has nuclear with some cytoplasmic positivity in all tissues throughout the body. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804; Cancer Res. 2005. 65:3011-3016, PMID: 15833825;