Date of this Version
Genetics 159: 557–569 (October 2001)
In Aspergillus nidulans, germinating conidia undergo multiple rounds of nuclear division before forming a septum. Previous genetic results suggest that the ability to separate nuclear division and septum formation depends upon a threshold level of activity of the cyclin-dependent kinase NIMXcdk1. Mutations in nimX and nimT, the gene encoding the NIMXcdk1-activating phosphatase, have revealed that Tyr-15 phosphorylation is important for determining the timing of the formation of the first septum. Here, we describe a screen for suppressors of nimT23 (snt), designed to identify additional components of the pathway regulating septum formation. We show that a subset of the snt mutants are defective in the temporal regulation of septum formation and in cell cycle checkpoint responses. Molecular characterization of sntA shows that it is allelic to the previously described ankA gene, which encodes the NIMXcdk1 Tyr-15 kinase. Additional experiments described in this study show that nutritional conditions modulate the timing of septum formation and alter the phenotypes displayed by the snt mutants. A model that suggests that the timing of septum formation is influenced by DNA damage and glucose availability via the sntA and sntB gene products is proposed.