Analysis of All Protein Phosphatase Genes in Aspergillus nidulans Identifies a New Mitotic Regulator, Fcp1†

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 phos-phatase catalytic subunit genes were identified. Systematic deletion analysis identified four essential phos-phatases 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 that nimT and bimG have essential functions required for mitotic progression since their deletions led to classical G2- and M-phase arrest. Although not as obvious, cells with AnpphA and Annem1 deleted also have mitotic abnormalities. One of the essential phosphatases, the RNA polymerase II C-terminal domain phosphatase Anfcp1, was further examined for potential functions in mitosis because a temperature-sensitive Anfcp1 allele was isolated in a genetic screen showing synthetic interaction with the cdk1Fmutation, a hyperactive mitotic kinase. The Anfcp1ts cdk1F double mutant had severe mitotic defects, including inability of nuclei to complete mitosis in a normal fashion. The severity of the Anfcp1ts cdk1F mitotic phenotypes were far greater than either single mutant, confirming the synthetic nature of their genetic interaction. The mitotic defects of the Anfcp1ts cdk1F double mutant suggest