A kinase-anchoring protein (AKAP)95 recruits human chromosome-associated protein (hCAP)-D2/Eg7 for chromosome condensation in mitotic extract

Association of the condensin multiprotein complex with chromatin is require d for chromosome condensation at mitosis. What regulates condensin targetin g to chromatin is largely unknown. We previously showed that the nuclear A kinase-anchoring protein, AKAP95, is implicated in chromosome condensation. We demonstrate here that AKAP95 acts as a targeting protein for human chro mosome-associated protein (hCAP)-D2/Eg7, a component of the human condensin complex, to chromosomes. In HeLa cell mitotic extract, AKAP95 redistribute s from the nuclear matrix to chromatin, When association of AKAP95 with chr omatin is prevented, the chromatin does not condense. Condensation is rescu ed by a recombinant AKAP95 peptide containing the 306 COOH-terminal amino a cids of AKAP95. Recombinant AKAP95 binds chromatin and elicits recruitment of Eg7 to chromosomes in a concentration-dependent manner. Amount of Eg7 re cruited correlates with extent of chromosome condensation: resolution into distinct chromosomes is obtained only when near-endogenous levels of Eg7 ar e recruited. Eg7 and AKAP95 immunofluorescently colocalize to the central r egion of methanol-fixed metaphase chromosomes. CST pull-down data also sugg est that AKAP95 recruits several condensin subunits. The results implicate AKAP95 as a receptor that assists condensin targeting to chromosomes.