In addition to the SR proteins, we found three other proteins that contain RS domains

ition to INCENP, MKLP2 is also hyperphosphorylated by Cdk1 prior to the metaphase-to-anaphase transition while it is rapidly dephosphorylated upon anaphase transition via PP1/PP2A. Cdk1 phosphorylation of MKLP2 is essential for maintaining spindle dynamics that are required for chromosome congression during early mitotic progression because phosphoresistant, but not phosphomimetic, mutants of MKLP2 in early mitotic cells prematurely bind microtubules and alter spindle dynamics by enhancing PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19811080 microtubule stability. Notably, Cdk1 phosphorylation of MKLP2 also controls the timely recruitment of MKLP2 to anaphase chromosomes, but the chromosome adaptor that recruits MKLP2 is unknown. When the stalk domain of MKLP2 that is responsible for its chromosome targeting is ectopically expressed, it blocks CPC relocation from anaphase chromosomes, suggesting that MKLP2 may be responsible for removing the CPC directly from anaphase chromosomes. How the spatiotemporal recognition between MKLP2 and the CPC occurs on anaphase chromosomes remains unclear. Furthermore, because MKLP2 has a strong microtubule bundling activity that is suppressed by Cdk1 phosphorylation, it is unclear how this chromosome targeting of MKLP2 upon anaphase onset occurs before its mitotic spindle binding and bundling. The interaction between MKLP2 and the CPC is mediated by the C-terminal cargo-binding domain of MKLP2. MKLP2 directly binds the N-terminal region of INCENP. Upon anaphase onset, reversing Cdk1/cyclin B1-dependent phosphorylation of MKLP2 is also essential for CPC relocation to the cell equator and for cytokinesis, which is similar to reversing Cdk1 phosphorylation of INCENP on Thr59. The 487-52-5 biological activity reason why Cdk1/cyclin B1 phosphoregulates both MKLP2 and INCENP is unclear. Notably, as Aurora B activity is also required for CPC relocation, inhibiting Aurora B activity also traps MKLP2 on anaphase chromosomes together with the CPC. Thus, it may be possible that Aurora B phosphorylation directly or indirectly activates the motor activity of MKLP2, or it may dissociate the CPC-bound MKLP2 from anaphase chromosomes. In addition, as discussed above, ubiquitination of Aurora B facilitates the active removal of Aurora B from anaphase chromosomes by the AAA+ ATPase and ubiquitin-dependent chaperone p97. However, it is unclear whether MKLP2 and Cdc48/p97 act in the same pathway for CPC relocation or whether they function independently to remove the CPC from anaphase chromosomes. Interestingly, in KLHL21depleted cells, MKLP2 localization to the spindle midzone is also reduced, which indicates a potential interdependency between MKLP2 and Cdc48/p97 in promoting CPC relocation. In S. cerevisiae, which lack MKLP2, Cdc28 -mediated phosphorylation of Ipl1/Aurora B suppresses its association with the microtubule plus-end tracking protein Bim1, which is a homolog of end-binding 1. This also inhibits Ipl1/Aurora B localization to the spindle midzone before anaphase onset. In addition, Ipl1/Aurora B relocation also depends on Cdc14 phosphatase, which dephosphorylates multiple Cdc28 and Ipl1/Aurora B sites mainly in the microtubule binding domain of Sli15/INCENP because phosphorylation of these sites inhibits microtubule binding of Sli15/INCENP prior to anaphase onset. It is unclear whether this mechanism is also conserved in mammalian cells, although the increase in microtubule binding affinity of the CPC is observed by dephosphorylation of Thr59 in INCENP. The Role of CPC Relocation as a Surveil