Fission Yeast rad12⁺Regulates Cell Cycle Checkpoint Control and Is Homologous to the Bloom’s Syndrome Disease Gene

ABSTRACT

The human BLM gene is a member of the Escherichia coli recQ helicase family, which includes the Saccharomyces cerevisiae SGS1 and human WRN genes. Defects in BLM are responsible for the human disease Bloom’s syndrome, which is characterized in part by genomic instability and a high incidence of cancer. Here we describe the cloning ofrad12⁺, which is the fission yeast homolog ofBLM and is identical to the recently reportedrhq1 ⁺ gene. We showed that rad12null cells are sensitive to DNA damage induced by UV light and γ radiation, as well as to the DNA synthesis inhibitor hydroxyurea. Overexpression of the wild-type rad12 ⁺ gene also leads to sensitivity to these agents and to defects associated with the loss of the S-phase and G₂-phase checkpoint control. We showed genetically and biochemically thatrad12 ⁺ acts upstream fromrad9 ⁺, one of the fission yeast G₂checkpoint control genes, in regulating exit from the S-phase checkpoint. The physical chromosome segregation defects seen in rad12 null cells combined with the checkpoint regulation defect seen in the rad12 ⁺ overproducer implicate rad12 ⁺ as a key coupler of chromosomal integrity with cell cycle progression.

ACKNOWLEDGMENTS

S.D. is a Career Scientist of the Cancer Care Ontario (CCO), and this work was supported in part by CCO startup funds and MRCC grant MT-14352 to S.D. G.A.F. is supported by NIH grant CA72647. H.B.L. is supported in part by an NIH Research Career Development Award (CA68446) and by NIH grants GM52493 and CA73043 and American Cancer Society grant CN-106.