DOMINANT-NEGATIVE CYCLIN-SELECTIVE UBIQUITIN CARRIER PROTEIN E2-C UBCH10 BLOCKS CELLS IN METAPHASE/

Destruction of mitotic cyclins by ubiquitin-dependent proteolysis is r equired for cells to complete mitosis and enter interphase of the next cell cycle, In clam eggs, this process is catalyzed by a cyclin-selec tive ubiquitin carrier protein, E2-C, and the cyclosome/anaphase promo ting complex (APC), a 20S particle containing cyclin-selective ubiquit in ligase activity, sere me report cloning a human homolog of E2-C, Ub cH10, which shares 61% amino acid identity with clam E2-C and can subs titute for clam E2-C in vitro. Dominant-negative clam E2-C and human U bcH10 proteins, created by altering the catalytic cysteine to serine, inhibit the in vitro ubiquitination and destruction of cyclin B in cla m oocyte extracts, When transfected into mammalian cells, mutant UbcH1 0 inhibits the destruction of both cyclin A and B, arrests cells in hi phase, and inhibits the onset of anaphase, presumably by blocking the ubiquitin-dependent proteolysis of proteins responsible for sister ch romatid separation, Thus, E2-C/UbcH10-mediated ubiquitination is invol ved in both cdc2 inactivation and sister chromatid separation, process es that are normally coordinated during exit from mitosis.