Mutations In SID2, A Novel Gene In Saccharomyces Cerevisiae, Cause Synthetic Lethality With sic1 Deletion And May Cause A Defect During S Phase

M. D. Jacobson
Claudia Ximena Muñoz 99, Swarthmore College
Kirstin Suzanne Knox 99, Swarthmore College
Beth Ellen Williams 01, Swarthmore College
Lenette Lin Lu 02, Swarthmore College
F. R. Cross
Elizabeth Ann Vallen, Swarthmore College

This work has been provided to PubMed Central courtesy of the Genetics Society of America.


SIC1 encodes a nonessential B-type cyclin/CDK inhibitor that functions at the G1/S transition and the exit from mitosis. To understand more completely the regulation of these transitions, Mutations causing synthetic lethality with sic1 Delta were isolated. In this screen, we identified a novel gene, SID2, which encodes an essential protein that appear., to be required for DNA replication or repair. sid2-1 sic1 Delta strains and sid2-21 temperature-sensitive strains arrest preanaphase as large-budded cells with a single nucleus, a short spindle, and an similar to 2C DNA content. RAD9, which is necessary for the DNA damage checkpoint, is required for the preanaphase arrest of sid2-1 sic1 Delta cells. Analysis of chromosomes in mutant sid2-21 cells by field inversion gel clectropiioresis suggests the presence of replication forks and bubbles at the arrest. Deleting the two S phase cyclins, CLB5 and CLB6, substantially suppresses the sid2-1 sir1 Delta inviability, while stabilizing Clb5 protein exacerbates the defects of sid2-1 sic1 Delta, cells. In synchronized sid2-1 mutant strains, the onset of replication appears normal, but completion of DNA synthesis is delayed. sid2-1 mutants are sensitive to hydroxytirea indicating that sid2-1 cells may suffer DNA damage that, when combined with additional insult, leads to a decrease in viability. Consistent with this hypothesis, sid2-1 rad9 cells are dead or very slow growing even when SIC1 is expressed.