Sadhu C, Hoekstra D, McEachern M J, Reed S I, Hicks J B
Department of Molecular Biology, Research Institute of Scripps Clinic, La Jolla, California 92037.
Mol Cell Biol. 1992 May;12(5):1977-85. doi: 10.1128/mcb.12.5.1977-1985.1992.
We have isolated a gene, designated CAG1, from Candida albicans by using the G-protein alpha-subunit clone SCG1 of Saccharomyces cerevisiae as a probe. Amino acid sequence comparison revealed that CAG1 is more homologous to SCG1 than to any other G protein reported so far. Homology between CAG1 and SCG1 not only includes the conserved guanine nucleotide binding domains but also spans the normally variable regions which are thought to be involved in interaction with the components of the specific signal transduction pathway. Furthermore, CAG1 contains a central domain, previously found only in SCG1. cag1 null mutants of C. albicans created by gene disruption produced no readily detectable phenotype. The C. albicans CAG1 gene complemented both the growth and mating defects of S. cerevisiae scg1 null mutants when carried on either a low- or high-copy-number plasmid. In diploid C. albicans, the CAG1 transcript was readily detectable in mycelial and yeast cells of both the white and opaque forms. However, the CAG1-specific transcript in S. cerevisiae transformants containing the C. albicans CAG1 gene was observed only in haploid cells. This transcription pattern matches that of SCG1 in S. cerevisiae and is caused by a1-alpha 2 mediated repression in diploid cells. That is, CAG1 behaves as a haploid-specific gene in S. cerevisiae, subject to control by the a1-alpha 2 mating-type regulation pathway. We infer from these results that C. albicans may have a signal transduction system analogous to that controlling mating type in S. cerevisiae or possibly even a sexual pathway that has so far remained undetected.
我们以酿酒酵母的G蛋白α亚基克隆SCG1为探针，从白色念珠菌中分离出一个名为CAG1的基因。氨基酸序列比较显示，CAG1与SCG1的同源性高于迄今报道的任何其他G蛋白。CAG1和SCG1之间的同源性不仅包括保守的鸟嘌呤核苷酸结合结构域，还跨越了通常可变的区域，这些区域被认为参与与特定信号转导途径成分的相互作用。此外，CAG1包含一个以前仅在SCG1中发现的中央结构域。通过基因敲除产生的白色念珠菌cag1缺失突变体没有产生易于检测到的表型。当携带低拷贝数或高拷贝数质粒时，白色念珠菌CAG1基因弥补了酿酒酵母scg1缺失突变体的生长和交配缺陷。在二倍体白色念珠菌中，在白色和不透明形式的菌丝体和酵母细胞中都很容易检测到CAG1转录本。然而，在含有白色念珠菌CAG1基因的酿酒酵母转化体中，仅在单倍体细胞中观察到CAG1特异性转录本。这种转录模式与酿酒酵母中SCG1的转录模式相匹配，并且是由二倍体细胞中a1-α2介导的抑制作用引起的。也就是说，CAG1在酿酒酵母中表现为单倍体特异性基因，受a1-α2交配型调控途径的控制。我们从这些结果推断，白色念珠菌可能具有类似于控制酿酒酵母交配型的信号转导系统，或者甚至可能有一个迄今尚未被发现的有性途径。
