Culotta V C, Howard W R, Liu X F
Department of Environmental Health Sciences, Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland 21205.
J Biol Chem. 1994 Oct 14;269(41):25295-302.
Protection from copper toxicity in the bakers' yeast Saccharomyces cerevisiae involves the action of a copper binding metallothionein encoded by the CUP1 locus. To identify additional factors contributing to copper ion homeostasis and detoxification, we screened a genomic library for genes that confer high levels of copper resistance to yeast strains lacking CUP1. This screen led to the identification of the CRS5 (copper-resistant suppressor) gene. By sequence analyses, CRS5 encodes a small molecular weight cysteine-rich protein with an amino acid sequence bearing all the features of a eukaryotic metallothionein. The CRS5 polypeptide exhibits a striking similarity to a number of mammalian and invertebrate metallothioneins, yet shares surprisingly little homology with CUP1. In yeast, CRS5 is expressed as a 0.5-kilobase mRNA that is regulated both by copper ions and by oxidative stress, and expression is dependent upon ACE1, a copper and DNA binding transcription factor also known to regulate CUP1. Deletion of the chromosomal CRS5 locus was found to increase cellular sensitivity to copper, but not cadmium, toxicity. These studies support an important role for the CRS5 metallothionein-like protein in copper homeostasis and detoxification.
酿酒酵母中对铜毒性的防护涉及由CUP1基因座编码的一种铜结合金属硫蛋白的作用。为了鉴定有助于铜离子稳态和解毒的其他因素，我们在基因组文库中筛选了赋予缺乏CUP1的酵母菌株高水平铜抗性的基因。该筛选导致鉴定出CRS5（抗铜抑制因子）基因。通过序列分析，CRS5编码一种小分子量的富含半胱氨酸的蛋白质，其氨基酸序列具有真核金属硫蛋白的所有特征。CRS5多肽与许多哺乳动物和无脊椎动物金属硫蛋白具有显著相似性，但与CUP1的同源性却惊人地低。在酵母中，CRS5以0.5千碱基的mRNA形式表达，该mRNA受铜离子和氧化应激调节，其表达依赖于ACE1，ACE1是一种铜和DNA结合转录因子，也已知可调节CUP1。发现染色体CRS5基因座的缺失会增加细胞对铜毒性的敏感性，但不会增加对镉毒性的敏感性。这些研究支持了CRS5金属硫蛋白样蛋白在铜稳态和解毒中的重要作用。
