TREX complex of at least 9 proteins (see below). The functional orchestration of this complex is important for the maintenance of the efficiency and fidelity of gene expression processes. The TREX (TRanscription-EXport) complex is an evolutionarily conserved multicomplex that plays a major role in the functional coupling of different steps during mRNA biogenesis, including mRNA transcription, processing, decay, and nuclear export. Furthermore, studies in mice have revealed that the metazoan TREX complex is required for cell differentiation and development, likely because this complex regulates the expression of key genes (Katahira 2012).