Mio T, Yamada-Okabe T, Yabe T, Nakajima T, Arisawa M, Yamada-Okabe H
Department of Mycology, Nippon Roche Research Center, Kamakura, Japan.
J Bacteriol. 1997 Apr;179(7):2363-72. doi: 10.1128/jb.179.7.2363-2372.1997.
Cell wall beta-glucan in a pathogenic fungus, Candida albicans, is highly branched with beta-1,3 and beta-1,6 linkages. We have isolated the C. albicans cDNAs for KRE6 and SKN1, the genes required for beta-1,6-glucan synthesis in Saccharomyces cerevisiae. The results of Northern blot analysis revealed that C. albicans KRE6 was expressed at a higher level than SKN1 in the yeast phase, while SKN1 expression was strongly induced upon induction of hyphal formation. In addition, the C. albicans KRE6 and SKN1 mRNAs but not the actin mRNA were shortened during the yeast-hypha transition. Unlike S. cerevisiae, more than 50% of cell wall glucan was beta-1,6 linked in C. albicans. Neither beta-1,3-glucan nor beta-1,6-glucan was affected by the homozygous C. albicans skn1 delta null mutation. Although we never succeeded in generating the homozygous C. albicans kre6 delta null mutant, the hemizygous kre6 delta mutation decreased the KRE6 mRNA level by about 60% and also caused a more than 80% reduction of beta-1,6-glucan without affecting beta-1,3-glucan. The physiological function of KRE6 was further examined by studying gene regulation in C. albicans. When KRE6 transcription was suppressed by using the HEX1 promoter, C. albicans cells exhibited the partial defect in cell separation and increased susceptibility to Calcofluor White. These results demonstrate that KRE6 plays important roles in beta-1,6-glucan synthesis and budding in C. albicans.
致病性真菌白色念珠菌的细胞壁β-葡聚糖具有高度分支，含有β-1,3和β-1,6连接键。我们已经分离出白色念珠菌中与酿酒酵母β-1,6-葡聚糖合成所需基因KRE6和SKN1相对应的cDNA。Northern印迹分析结果显示，白色念珠菌KRE6在酵母阶段的表达水平高于SKN1，而SKN1的表达在菌丝形成诱导后被强烈诱导。此外，在酵母-菌丝转变过程中，白色念珠菌KRE6和SKN1的mRNA缩短了，但肌动蛋白mRNA没有缩短。与酿酒酵母不同，白色念珠菌中超过50%的细胞壁葡聚糖是β-1,6连接的。纯合的白色念珠菌skn1Δ缺失突变对β-1,3-葡聚糖和β-1,6-葡聚糖均无影响。尽管我们从未成功构建出纯合的白色念珠菌kre6Δ缺失突变体，但半合子kre6Δ突变使KRE6 mRNA水平降低了约60%，同时导致β-1,6-葡聚糖减少了80%以上，而不影响β-1,3-葡聚糖。通过研究白色念珠菌中的基因调控，进一步考察了KRE6的生理功能。当使用HEX1启动子抑制KRE6转录时，白色念珠菌细胞在细胞分离方面表现出部分缺陷，并且对荧光增白剂的敏感性增加。这些结果表明，KRE6在白色念珠菌的β-1,6-葡聚糖合成和出芽过程中发挥着重要作用。
