Abstract #93C

Characterization of cytokinesis mutants in Saccharomyces cerevisiae. Elizabeth A Vallen¹, Lydia Thé¹, Jianying Luo², Nile Chang¹, Colin Palmer¹, Stacey Prow¹, Peter Yang¹, Margaret Lippincott¹, Masayuki Iwase², Erfei Bi². 1) Biology, Swarthmore College, Swarthmore, PA; 2) Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA.
   Cytokinesis in Saccharomyces cerevisiae occurs via the coordinated action of the actomyosin contractile ring and the septum-formation process. Although the actomyosin contractile ring is not essential in some strain backgrounds, it is required for cytokinesis and viability in strains deleted for HOF1, a gene important for coordinating the ring function and septum formation (Vallen, Caviston and Bi, 2000 Mol. Biol. Cell, 11:593-611). A screen for mutants synthetically lethal with hof1 was utilized to identify and characterize proteins required for the function of the actomyosin ring or other steps in cytokinesis. Approximately 40 HOF1-dependent mutants were identified by screening 33,000 mutagenized colonies using a sectoring assay and other genetic tests.
    Complementation testing, linkage analysis, plasmid-linked suppression and DNA sequencing indicate that mutations were isolated in BNI1, BNI5, CYK3, ELM1, GIN4, MLC1, MYO1, and PSA1. Some mutants have yet to be characterized.
    A subset of the myo1 alleles has been analyzed in more detail. A number of the isolated mutations are premature stop codons occurring in the C-terminal quarter of the protein. Preliminary data analyzing GFP-myo1p suggests these proteins localize to the bud neck and that at least some of the mutant strains have actin rings as visualized by staining with rhodamine-labeled phallodin. This suggests that these mutations are not complete loss-of-function alleles.

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