Analysis of all protein phosphatase genes in Aspergillus nidulans identifies a new mitotic regulator, Fcp1.


Son S, Osmani SA.

Date: 24 February 2009


Reversible protein phosphorylation is an important regulatory mechanism of cell cycle control in which protein phosphatases counteract the activities of protein kinases. In Aspergillus nidulans 28 protein phosphatase catalytic subunit genes were identified. Systematic deletion analysis identified four essential phosphatases and four required for normal growth. Conditional alleles of these were generated using the alcA promoter. The deleted phosphatase strain collection, and regulatable versions of the essential and near essential phosphatases, provide an important resource for further analysis of the role of reversible protein phosphorylation to the biology of A. nidulans. We further demonstrate nimT and bimG have essential functions required for mitotic progression as their deletions led to classical G2 and M phase arrest. While not as obvious, An-pphA and An-nem1 deleted cells also have mitotic abnormalities. One of the essential phosphatases, the RNA polymerase II C-terminal domain phosphatase An-fcp1, was further examined for potential functions in mitosis because a temperature sensitive An-fcp1 allele was isolated in a genetic screen showing synthetic interaction with the cdk1F mutation, a hyperactive mitotic kinase. The An-fcp1(ts) + cdk1F double mutant had severe mitotic defects including inability of nuclei to complete mitosis in a normal fashion. The severity of the An-fcp1(ts) + cdk1F mitotic phenotypes were far greater than either single mutant, confirming the synthetic nature of their genetic interaction. The mitotic defects of the An-fcp1(ts) + cdk1F double mutant suggests a previously unrealized function for An-FCP1 in regulating mitotic progression, perhaps counteracting Cdk1 mediated phosphorylation.

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