Required for efficient export of polyadenylated RNA. 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. 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 (By similarity). Interacts with NIF3L1 (PubMed:12951069). Interacts with THOC5 (By similarity). Interaction with THOC5 is required for nuclear localization. Ubiquitously expressed. Expressed at low levels in testis between P3 and P14. Expression in testis increases at P20 and reaches maximum levels in adult. Belongs to the THOC7 family.