The Cryptococcus neoformans STE11α gene is similar to other fungal mitogen-activated protein kinase kinase kinase (MAPKKK) genes but is mating type specific

Partial sequence analysis of the Cryptococcus neoformans MAT alpha mating type locus revealed the presence of a gene with substantial sequence similarity to other fungal mitogen-activated protein (MAP) kinase kinase kinase (MAPKKK) genes, The C. neoformans gene, designated STE11 alpha, showed the highest degree of similarity to the Neurospora crassa nrc-l, Schizosaccharomyces pombe byr2 and Saccharomyces cerevisiae STE11 genes. A polymerase chain reaction-mediated sib-selection technique was successfully adapted for the purpose of disrupting STE11 alpha. C. neoformans ste11 alpha Delta mutants were found to be sterile, consistent with the phenotypes of ste11 and byr2 mutants in S. cerevisiae end S. pombe respectively. Haploid ste11 alpha Delta mutants were also found to be unable to produce hyphae, suggesting that the C. neoformans gene is functionally conserved when compared with its S. cerevisiae MAPKKK counterpart. Comparison of the wild-type STE11 alpha strain with a ste11 alpha Delta disruptant for virulence using the mouse model showed that the ste11 alpha Delta strain was less virulent, but the difference was only minor. In spite of some of the conserved functions of STE11 alpha, linkage analysis showed that STE11 alpha is only found in mating type alpha strains, These results demonstrate that, although functionally conserved, the mating pathway in C. neoformans has a unique organization.