A putative N-terminal nuclear export sequence is sufficient for Mps1 nuclear exclusion during interphase

Background: Mps1, an essential component of the mitotic checkpoint, is also an important interphase regulator and has roles in DNA damage response, cytokinesis and centrosome duplication. Mps1 predominantly resides in the cytoplasm and relocates into the nucleus at the late G2 phase. So far, the mechanism underlying the Mps1 translocation between the cytoplasm and nucleus has been unclear. Results: In this work, a dynamic export process of Mps1 from the nucleus to cytoplasm in interphase was revealed-a process blocked by the Crm1 inhibitor, Leptomycin B, suggesting that export of Mps1 is Crm1 dependent. Consistent with this speculation, a direct association between Mps1 and Crm1 was found. Furthermore, a putative nuclear export sequence (pNES) motif at the N-terminal of Mps1 was identified by analyzing the motif of Mps1. This motif shows a high sequence similarity to the classic NES, a fusion of this motif with EGFP results in dramatic exclusion of the fusion protein from the nucleus. Additionally, Mps1 mutant loss of pNES integrity was shown by replacing leucine with alanine which produced a diffused subcellular distribution, compared to the wild type protein which resides predominantly in cytoplasm. Conclusion: Taken these findings together, it was concluded that the pNES sequence is sufficient for the Mps1 export from nucleus during interphase.