The STE12alpha gene of Cryptococcus neoformans encodes a protein containing both homeodomain and zinc finger regions. As homeodomains and zinc finger regions are important domains for the function of many transcription factors, we used site-specific mutagenesis to delineate the roles of these two domains. The homeodomain and zinc finger regions are each important for the function of Ste12alphap. DNA binding ability, mating frequency, and haploid fruiting capability were reduced in strains with mutations in the homeodomain, whereas virulence and capsule size in the mouse brain were increased. In contrast, mutations in the zinc fingers region resulted in decreased virulence, reduced capsule size in the mouse brain and decreased gene expression of capsule associated genes. In addition, phospholipase activity was increased in the zinc finger mutants. Taken together, most of the phenotypes previously observed in the ste12alpha deletion strains were reproduced in these two types of mutants. However, unlike mutations in the homeodomain/zinc finger region, complete deletion of STE12alpha caused a severe reduction in virulence and a decrease in phospholipase activity. These data suggest that region(s) other than the homeodomain and zinc finger regions of Ste12alphap contribute to the variable influences on the different phenotypes observed in C. neoformans.
Copyright 2004 Blackwell Publishing Ltd