The Phosphotyrosyl Phosphatase Activator, Ncs1p (Rrd1p), Functions with Cla4p To Regulate the G2/M Transition in Saccharomyces cerevisiae
Open Access
- 1 January 2001
- journal article
- Published by Taylor & Francis in Molecular and Cellular Biology
- Vol. 21 (2), 488-500
- https://doi.org/10.1128/mcb.21.2.488-500.2001
Abstract
The Saccharomyces cerevisiae p21-activated kinases, Ste20p and Cla4p, have individual functions but appear to share an essential function(s) as well because a strain lacking both kinases is inviable. To learn more about the shared function, we sought new mutations that were lethal in the absence of CLA4. This approach led to the identification of at least 10 complementation groups designated NCS (need CLA4 to survive). As for ste20 cla4-75 mutants, most ncs cla4-75double mutants were defective for septin localization during budding. One group, NCS1/RRD1 (YIL153w), did not confer this defect, however, and we investigated its function further.ncs1Δ cla4Δ cells arrested with elongated buds and short mitotic spindles. The morphological defects and lethality were suppressed by mutations that abrogate the cell cycle morphogenetic checkpoint, CDC28Y19F or swe1Δ. The connection to the cell cycle may be direct, as we detected a Cla4p-Cdc28p complex. NCS1 encodes a protein with significant similarity to a mammalian phosphotyrosyl phosphatase activator (PTPA) regulatory subunit for type 2A protein phosphatases (PP2As). Genetic and biochemical evidence suggested that the phosphatase Sit4p is a target for Ncs1p. First, CLA4 andSIT4 were synthetically lethal. Second, Ncs1p and its yeast paralog, Noh1p (Rrd2p), bound to the catalytic domain of Sit4p in vitro, and Ncs1p could be immunoprecipitated with Sit4p but not with another PP2A (Pph21p) from yeast cell extracts. Strains lacking bothNCS1 and NOH1 were inviable and arrested as unbudded cells, implying that PTPA function is required for proper G1 progression.Keywords
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