Characteristics of Chromosome Breakage in Fission Yeast S. pombe
By: Jiayu Luo
Department: Biology
Faculty Advisor: Dr. Sally Pasion
Chromosome instability often leads to cell death or increased susceptibility of cancers and tumors. Cdc24p, encoded by cdc24+ in S. pombe, interacts with many evolutionarily conserved replication proteins, such as DNA ligase, DNA helicase and PCNA. cdc24 truncation mutants (cdc24-M38 and cdc24-G1) showed chromosome fragmentation at the restrictive temperature (34℃). However, it is unknown during which phase of the cell division cycle that cdc24 mutants break chromosomes. In this study, we report that asynchronous cdc24 point mutant (cdc24-M81) also have chromosome fragmentation at the restrictive temperature. We also demonstrate that both cdc24 and cdc17 mutants have delay in S-phase progression at the permissive temperature (25℃). Moreover, we used nda3 mutation to arrest cdc24 cells in mitosis and determine replication timing of the cdc24nda3 mutants. We found that the cdc24-M38nda3 double mutant cell were peaked in S phase (45.2% of cells in S phase) after 2.5 hours release at 25℃. We then use PFGE to determine chromosome integrity in cdc24 mutants that are enriched in mitosis and S phase. We found that cdc24-M38nda3 mutants do not have chromosome fragmentation when 40.6% of the cells are in S phase. It suggests that, at the restrictive temperature, cdc24 mutants do not break chromosomes during mitosis and S phase of the cell cycle.