Tanaka K, Nakafuku M, Tamanoi F, Kaziro Y, Matsumoto K, Toh-e A
Department of Fermentation Technology, Faculty of Engineering, Hiroshima University, Japan.
Mol Cell Biol. 1990 Aug;10(8):4303-13. doi: 10.1128/mcb.10.8.4303-4313.1990.
The IRA1 gene is a negative regulator of the RAS-cyclic AMP pathway in Saccharomyces cerevisiae. To identify other genes involved in this pathway, we screened yeast genomic DNA libraries for genes that can suppress the heat shock sensitivity of the ira1 mutation on a multicopy vector. We identified IRA2, encoding a protein of 3,079 amino acids, that is 45% identical to the IRA1 protein. The region homologous between the IRA1 protein and ras GTPase-activating protein is also conserved in IRA2. IRA2 maps 11 centimorgans distal to the arg1 locus on the left arm of chromosome XV and was found to be allelic to glc4. Disruption of the IRA2 gene resulted in (i) increased sensitivity to heat shock and nitrogen starvation, (ii) sporulation defects, and (iii) suppression of the lethality of the cdc25 mutant. Analysis of disruption mutants of IRA1 and IRA2 indicated that IRA1 and IRA2 proteins additively regulate the RAS-cyclic AMP pathway in a negative fashion. Expression of the IRA2 domain homologous with GAP is sufficient for complementation of the heat shock sensitivity of ira2, suggesting that IRA down regulates RAS activity by stimulating the GTPase activity of RAS proteins.
IRA1基因是酿酒酵母中RAS-环磷酸腺苷途径的负调控因子。为了鉴定参与该途径的其他基因，我们在酵母基因组DNA文库中筛选能够在多拷贝载体上抑制ira1突变体热休克敏感性的基因。我们鉴定出了IRA2基因，它编码一种由3079个氨基酸组成的蛋白质，与IRA1蛋白有45%的同源性。IRA1蛋白与ras GTP酶激活蛋白之间的同源区域在IRA2中也保守存在。IRA2基因定位于第十五号染色体左臂上arg1基因座远端11厘摩处，并且发现它与glc4等位。IRA2基因的破坏导致：（i）对热休克和氮饥饿的敏感性增加；（ii）孢子形成缺陷；（iii）抑制cdc25突变体的致死性。对IRA1和IRA2破坏突变体的分析表明，IRA1和IRA2蛋白以负向方式累加调节RAS-环磷酸腺苷途径。与GAP同源的IRA2结构域的表达足以互补ira2的热休克敏感性，这表明IRA通过刺激RAS蛋白的GTP酶活性来下调RAS活性。
