Cell biology analyses on the synthesis and localization of the proteins in fungal cells

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1. Biochemical studies on the detection of intracellular forms of secreted aspartic proteinase in Candida albicans. C. albicans secretes acid proteinase (EPR) in the medium which contains bovine serum albumin as a sole source of nitrogen. By immunoblotting with anti-EPR serum, 43 and 45 kDa proteins were detected in the cytoplasmic fraction, which recovered from the different membrane fractions. 45 kDa would be a precursor of the secreting 43 kDa protein. 2. Ultrastructure studies on the proteinase secreting cells by alkaline bismuth staining and immunocytochemistry. We found many flocculent granules at the cell periphery of the proteinase-secreting cells, but the granules were not specific for the secretion. This was deduced from observations of alkaline bismuth staining, of effects of a secretion inhibitor Brefeldin A, and of immunoelectron microscopy using anti-EPR serum. 3. Biochemical studies on the induction of extracellular proteinase (EPR) in Candida albicans. It was shown that EPR was induced without the addition of nitrogen source so long as glucose as a carbon source is present, and not induced at a pH greater than 6.0 irrespective of the presence of nitrogen source. the results suggested EPR production and germ tube formation play different roles in the invasive process. 4. Studies on the behavior of F-actin in Schizosaccharomyces pombe by fluorescent and electron microscopy. (i) Starvation in distilled water dispersed the actin dots localized at the cell ends into thick patches and cables throughout the cytoplasm. (ii) Cytochalasin A inhibited the appearance of actin ring at a cell equator before septum formation and cytoplasmic vesicles and dictyosomes were altered in to dense bodies in the cytoplasm. Actin network maintains the organization of the secretory pathway involving dictyosomes and vesicles.