CELL-DIVISION CYCLE MUTANTS ALTERED IN DNA-REPLICATION AND MITOSIS IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

A total of 59 new temperature sensitive cdc mutants are described which grow normally at 25.degree. C but become blocked at DNA replication or mitosis when incubated at 36.degree. C. Thirty-nine of the mutants are altered in cdc genes identified previously. The remaining 20 mutants define 20 new cdc genes. These were characterized physiologically; 6 of the genes (cdc 17, 20, 21, 22, 23, 24) were requried for DNA replication 2 for mitosis (cdc 27, 28) and 2 (cdc 18, 19) could not be assigned to either DNA replication or mitosis but were definitely required for one or the other. Three genes, cdc 10 and cdc 20, 22, are likely to be required for the initiation of DNA replication. Mutants in 2 genes, cdc 17, 24, undergo bulk DNA synthesis at 36.degree. C, but this DNA is defective. In the case of cdc 17 the defect is in the ligation of Okazaki fragments. cdc 23 is required for bulk DNA synthesis, while cdc 21 may be required for the initiation of a particular sub-set of replicons. A previously isolated mutant cdc 13.117 is further described. This mutant becomes blocked in the middle of mitosis with apparently condensed chromosomes.