Browsing by Author "Bester, Michael C. (Michael Christiaan)"

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    Functional characterisation of Mss11p, a transcriptional regulator of pseudohyphal development, starch degradation and flocculation in Saccharomyces cerevisiae
    (Stellenbosch : Stellenbosch University, 2003-03) Bester, Michael C. (Michael Christiaan); Pretorius, I. S.; Nieuwoudt, Helene; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: The yeast Saccharomyces cerevisiae is able to sense and respond to changes in its immediate environment. Information regarding the nutritional status of the extracellular environment is sensed by membrane receptor systems and relayed through signalling pathways to the nuclear interior, affecting the transcription of specific genes., Transcription factors, which function downstream of these signal transduction pathways, have to be transported into the nucleus after synthesis in the cytoplasm in order to regulate transcriptional events. Transport into the nucleus occurs in a tightly regulated manner at the nuclear pore complex, which is located in the nuclear membrane, and requires the recognition of transport signal sequences, which are present in the proteins that are to be transported. Signalling pathways control the nuclear accessibility of transcriptional regulators by modifying their respective signal sequences. In response to a limited availability of carbon or nitrogen, cells are able to change their morphology from a unicellular ovoid form to elongated cells attached to each other. This morphological change is associated with daughter cells that remain attached to their respective mother cells following unipolar budding, thus forming filamentous structures referred to as pseudohyphae. The regulation of the development of pseudohyphae is correlated with other physiological processes, such as starch degradation and the invasion of agar-containing media. Mss11p performs a central role in the regulation of the genes required for these processes and it has been shown to specifically regulate the expression of FL011, which encodes a cell surface protein critical for pseudohyphal development, and STA2, which encodes an extracellular glucoamylase functioning in the degradation of starch. The aim of this study was to characterise the functioning of Mss11p. Overexpression analysis indicates that Mss11p functions as an inducer of invasive growth, cell elongation and flocculation. Furthermore, MSS11 deletion improves biomass formation and suppresses the growth defect of yeast from a L:1278b genetic background transformed with the RAS2val19 allele on non-fermentable carbon sources. Biochemical analysis shows that Mss11p is a nuclear protein of approximately 97 kDa in apparent size that is maintained at relatively low levels in yeast. Finally, the data suggest a model in which Mss11p functions as a mediator of the transcriptional regulation of various genes.