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Analysis of the hgl1 gene of Ustilago maydis Laidlaw, Robert David


The cAMP/protein kinase A signal transduction pathway plays an important role in morphogenesis in fungi. Previous work identified a gene encoding a Ustilago maydis homologue of the catalytic subunit of protein kinase A, adr1, involved in maintaining budding growth and virulence. The filamentous phenotype of an adr1- mutant was used in a genetic screen for suppressor mutations to identify components of the pathway downstream of protein kinase A. This screen resulted in the recovery of a mutation in hgl1 (hyphal growth locus 1). hgl1- mutants display a number of phenotypes including suppression of the filamentous growth of an adr1- mutant, the production of a yellow pigment, and a failure to complete the sexual phase of the life cycle. There are no similar proteins to Hgl1p in current databases and it is therefore difficult to identify its function by comparison to known genes. To identify a functional role for hgl1, additional characterization studies have been conducted including further analysis of the predicted amino acid sequence, phosphorylation experiments, and mutagenesis to isolate suppressors of hgl1-. The work in this thesis demonstrates that a reversion to the adr1- phenotype could be obtained through the collection of hgl1- suppressor mutants. Additional studies demonstrated that Hgl1p serves as a direct target for phosphorylation by Ustilago maydis protein kinase A in vitro. Analysis of the Hgl1p sequence revealed several interesting features of the protein which will be relevant for future experimentation. [Scientific formulae used in this abstract could not be reproduced.]

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