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. TREX is recruited to spliced mRNAs by a transcription-independent mechanism, binds to mRNA upstream of the exon-junction complex (EJC) and is recruited in a splicing- and cap-dependent manner to a region near the 5' end of the mRNA where it functions in mRNA export to the cytoplasm via the TAP/NFX1 pathway. THOC5 in conjunction with ALYREF/THOC4 functions in NXF1-NXT1 mediated nuclear export of HSP70 mRNA; both proteins enhance the RNA binding activity of NXF1 and are required for NXF1 localization to the nuclear rim. Involved in transcription elongation and genome stability. Involved in alternative polyadenylation site choice by recruiting CPSF6 to 5' region of target genes; probably mediates association of the TREX and CFIm complexes. Regulates the expression of myeloid transcription factors CEBPA, CEBPB and GAB2 by enhancing the levels of phosphatidylinositol 3,4,5-trisphosphate. May be involved in the differentiation of granulocytes and adipocytes. Essential for hematopoietic primitive cell survival and plays an integral role in monocytic development. Interacts with phosphorylated CSF1R (PubMed:10597251). Component of the THO complex, which is composed of THOC1, THOC2, THOC3, THOC5, THOC6 and THOC7; together with at least ALYREF/THOC4, DDX39B, SARNP/CIP29 and CHTOP, THO forms the transcription/export (TREX) complex which seems to have a dynamic structure involving ATP-dependent remodeling. Interacts with ALYREF/THOC4, and THOC7. Interacts (via N-terminus) with the NTF2 domain of NXF1 (By similarity). Forms a complex with CEBPB (PubMed:19015024). Interacts with CPSF6; indicative for an association with the cleavage factor Im (CFIm) complex (By similarity). Interacts with THOC1 (PubMed:16909111). Interacts with LUZP4 (By similarity). Interacts with NCBP3 (By similarity). Shuttles between nucleus and cytoplasm. Ubiquitously expressed, with highest levels in testis, liver and heart. Up-regulated following CSF1 stimulation. Phosphorylated on tyrosine upon binding to activated CSF1R; which causes a dissociation of the two proteins. Phosphorylation on Ser-5 and/or Ser-6 is required for nuclear export. Phosphorylated on Thr-328 in insulin-stimulated adipocytes. Embryonic lethality seen before day 5.5 of embryonic development (E5.5). Belongs to the THOC5 family.