Ohya Y, Caplin B E, Qadota H, Tibbetts M F, Anraku Y, Pringle J R, Marshall M S
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Japan.
Mol Gen Genet. 1996 Aug 27;252(1-2):1-10.
The gene CAL1 (also known as CDC43) of Saccharomyces cerevisiae encodes the beta subunit of geranylgeranyl transferase I (GGTase I), which modifies several small GTPases. Biochemical analyses of the mutant enzymes encoded by cal1-1, and cdc43-2 to cdc43-7, expressed in bacteria, have shown that all of the mutant enzymes possess reduced activity, and that none shows temperature-sensitive enzymatic activities. Nonetheless, all of the cal1/cdc43 mutants show temperature-sensitive growth phenotypes. Increase in soluble pools of the small GTPases was observed in the yeast mutant cells at the restrictive temperature in vivo, suggesting that the yeast prenylation pathway itself is temperature sensitive. The cal1-1 mutation, located most proximal to the C-terminus of the protein, differs from the other cdc43 mutations in several respects. An increase in soluble Rho1p was observed in the cal1-1 strain grown at the restrictive temperature. The temperature-sensitive phenotype of cal1-1 is most efficiently suppressed by overproduction of Rho1p. Overproduction of the other essential target, Cdc42p, in contrast, is deleterious in cal1-1 cells, but not in other cdc43 mutants or the wild-type strains. The cdc43-5 mutant cells accumulate Cdc42p in soluble pools and cdc43-5 is suppressed by overproduction of Cdc42p. Thus, several phenotypic differences are observed among the cal1/cdc43 mutations, possibly due to alterations in substrate specificity caused by the mutations.
酿酒酵母的CAL1基因（也称为CDC43）编码香叶基香叶基转移酶I（GGTase I）的β亚基，该酶可修饰多种小GTP酶。对在细菌中表达的由cal1-1以及cdc43-2至cdc43-7编码的突变酶进行的生化分析表明，所有突变酶的活性均降低，且均未表现出温度敏感性酶活性。尽管如此，所有cal1/cdc43突变体均表现出温度敏感性生长表型。在体内限制温度下，在酵母突变细胞中观察到小GTP酶的可溶性池增加，这表明酵母异戊二烯化途径本身对温度敏感。位于蛋白质C末端最靠近处的cal1-1突变在几个方面与其他cdc43突变不同。在限制温度下生长的cal1-1菌株中观察到可溶性Rho1p增加。Rho1p的过量表达最有效地抑制了cal1-1的温度敏感性表型。相比之下，另一个必需靶标Cdc42p的过量表达在cal1-1细胞中是有害的，但在其他cdc43突变体或野生型菌株中则不然。cdc43-5突变细胞在可溶性池中积累Cdc42p，并且cdc43-5被Cdc42p的过量表达所抑制。因此，在cal1/cdc43突变之间观察到几种表型差异，这可能是由于突变导致底物特异性改变所致。
