The <scp>THO</scp> complex in <i>Schizosaccharomyces pombe</i> —dissecting the composition and functional hierarchy

The THO complex was initially identified in Saccharomyces cerevisiae with five subunits: Hpr1p, Tho2p, Mft1p, Thp2p, and Tex1p. It plays a major role in mRNA processing and nuclear export. Here, we aimed to identify the putative homologs in Schizosaccharomyces pombe. Among eight candidates, genetic analysis showed tho1, tho2, and pci2 are essential, while mutants of tho5 and tho7 exhibited growth defects along with genome instability and impaired mRNA export. Subcellular localization studies showed all putative homologs except Tho3 are localized to the nucleus, whereas Pci2 localizes to the nuclear envelope. Yeast two-hybrid and immunoprecipitation-mass spectrometry confirmed Tho1, Tho2, Tho5, and Tho7 form the core THO complex. This work defines the THOC complex in S. pombe and supports Pci2 as a component of TREX-2 at the nuclear periphery during mRNA export.