Acts as component of the THO subcomplex of the TREX complex which is thought to couple mRNA transcription, processing and nuclear export. Component of the THO complex, which is composed of THO1, THO2, THO3, THO5, THO6 and THO7. A number of isoforms are produced. According to EST sequences. Embryonic lethality when homozygous. Belongs to the THOC2 family. Was originally thought to correspond to two different genes. Was originally thought to correspond to two different genes.