IS THE YEAST ANAPHASE PROMOTING COMPLEX NEEDED TO PREVENT RE-REPLICATION DURING G(2)-PHASE AND M-PHASE

The Anaphase Promoting Complex (APC) is required for anaphase progress ion and B-type cyclin proteolysis, The recent finding that inactivatio n of the APC allows 'over-replication' of DNA has led to the proposal that the APC might also be required for preventing reduplication of ch romosomes during G(2) and M phases. In this report we re-investigate t he phenotype of ape mutant cells and find that they do not re-replicat e their DNA during the period taken for wild-type cells to traverse G( 2) and M phases, ape mutants do, however, gradually increase their DNA content after long periods of cell cycle arrest, Such DNA synthesis o ccurs almost exclusively in the cytoplasm and neither occurs in cells lacking mitochondrial DNA nor depends on Cdc6, a protein which is esse ntial for the initiation of chromosomal but not mitochondrial DNA repl ication. ARS1, a chromosomal replication origin, is not re-fired in ce lls deprived of APC function, confirming that the 'over-replicated' DN A in ape mutant cells is of mitochondrial origin, Furthermore, we find that APC function is required to promote but not to prevent rereplica tion in ndc10 mutant cells. We therefore propose that the APC is not i nvolved in preventing re-duplication of chromosomes during G(2) and M phases.