Interdomain Interactions of the PCID2 Protein, One of the Subunits of the TREX-2 mRNA Export Complex in Drosophila melanogaster.

The TREX-2 complex is responsible for the export of mRNA from the nucleus to the cytoplasm and consists of four proteins. It was recently shown that the PCID2 subunit of TREX-2 is responsible for the specific recognition of mRNA by the TREX-2 complex. The majority of the protein contains the PCI domain, which has surfaces for RNA binding. The PCI domain includes the central region of the protein, which has a surface for non-specific RNA binding, M-PCID2, and the C-terminal part of the PCI domain and the C-terminal part of the protein, C-PCID2, which has a surface for specific RNA recognition. The N-terminal part of PCID2 contains a region whose function is unknown. Since the TREX-2 complex binds to only a specific mRNA and only at a specific stage, we hypothesized that the N-terminal part of PCID2 might modulate the binding of C-PCID2 to RNA by binding to it and covering its RNA-binding domain. We showed that the N-terminal region interacts with C-PCID2. The binding of C-PCID2 to RNA in this case is not impaired. In addition, the binding of C-PCID2 to RNA does not disrupt its interaction with the N-terminal part of the protein (N-PCID2). Thus, C-PCID2 can interact with N-PCID2 and RNA by different surfaces. This intrinsic interaction is probably necessary at one of the stages of functioning of the TREX-2 complex.