Molecular characterization of the proteins involved in the regulation of cell polarity in budding yeast and fission yeast

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I studied about the regulatory mechanisms of cell polarity in budding yeast and fission yeast.1.In budding yeast, cell type determines two distinct spatial budding patterns. Haploid cells exhibit an axial pattern, whereas diploid cells exhibit a bipolar pattern. Axl1 is the key morphological determinant for the haploid axial pattern. I identified a gene, RAX1, whose loss of function suppresses the defective bipolar pattern of axi1 haploids to the axial pattern, Rax1 is a long-lived protein persisting at division site remnants for multiple generations. Rax1 is required for the localization of Bud8. Rax1 is necessary for the establishment of the bipolar budding landmark.2.I constructed a gene library for random gene disruptions in fission yeast However, this library could not be useful for random gene disruption because some clones could replicate as plasmids in cells of fission yeast.3.I identified several genes involved in the regulation of cell polarity in fission yeast using cDNA overexpression library. Genes, tpb1,ckb1 and mid2,were characterized by two-hybrid analysis, gene disruption and microscopic analysis. The PB1 domain of Tpb1 interacts with that of Scd2. Cells of mid2 mutant strain could not exhibit new-end growth. However, overexpression of ckb1 caused new-end growth in mid2 mutant cells.4.In response to nitrogen limitation, diploid cells of budding yeast undergo a dimorphic transition to a filamentous growth form known as pseudohyphal growth. I identified a yeast gene, SFG1,whose overexpression enhances superficial pseudohyphal growth when starved for nitrogen. Sfg1 has a sequence similarity to members of a family of transcriptional regulators of fungal development. Cells of SFG1-disrupted strain have a serious defect in pseudohyphal growth. Sfg1 may act separately from mitogen-activated protein kinase pathway and cAMP-dependent protein kinase A pathway.