LOCALIZATION OF MOTOR-RELATED PROTEINS AND ASSOCIATED COMPLEXES TO ACTIVE, BUT NOT INACTIVE, CENTROMERES

Multicentric chromosomes are often found in tumor cells and certain ce ll lines, How they are generated is not fully understood, though their stability suggests that they are non-functional during chromosome seg regation, Growing evidence has implicated microtubule motor proteins i n attachment of chromosomes to the mitotic spindle and in chromosome m ovement, To better understand the molecular basis for the inactivity o f centromeres associated with secondary constrictions, we have tested these structures by immunofluorescence microscopy for the presence of motor complexes and associated proteins, We find strong immunoreactivi ty at the active, but not inactive, centromeres of prometaphase multic entric chromosomes using antibodies to the cytoplasmic dynein intermed iate chains, three components of the dynactin complex (dynamitin, Arp1 and p150(Glued)), the kinesin-related proteins CENP-E and MCAK and th e proposed structural and checkpoint proteins HZW10, CENP-F and Mad2p, These results offer new insight into the assembly and composition of both primary and secondary constrictions and provide a molecular basis for the apparent inactivity of the latter during chromosome segregati on.