The Mitotic Checkpoint Protein hBUB3 and the mRNA Export Factor hRAE1 Interact with GLE2p-binding Sequence (GLEBS)-containing Proteins

The mRNA export factor RAE1 (also called GLE2) and the mitotic checkpoint protein BUB3 share extensive sequence homology in yeast as well as higher eukaryotes, although the biological relevance of their similarity is unclear. Previous work in HeLa cells has shown that human (h)RAE1 binds the nuclear pore complex protein hNUP98 via a short NUP98 motif called GLEBS (for GLE2p-binding sequence). Here we report that the two known binding partners of hBUB3, the mitotic checkpoint proteins hBUB1 and hBUBR1, both carry a region with remarkable similarity to the GLEBS motif of hNUP98. We show that the GLEBS-like motifs of mouse (m)BUB1 and mBUBR1 are sufficient for mBUB3 binding. mBUB3 lacks affinity for the hNUP98 GLEBS, demonstrating its binding specificity for GLEBS motifs of mitotic checkpoint proteins. Interestingly, mRAE1 does not exclusively bind to the GLEBS motif of hNUP98 and can cross-interact with the mBUB1 GLEBS. We show that full-length RAE1 and BUB1 proteins interact in mammalian cells and accumulate both at the kinetochores of prometaphase chromosomes. Our findings demonstrate that GLEBS motifs reside in mammalian nucleoporins and mitotic checkpoint proteins and apparently serve as specific binding sites for either BUB3, RAE1, or both.