Costigan C, Kolodrubetz D, Snyder M
Department of Biology, Yale University, New Haven, Connecticut 06520-8103.
Mol Cell Biol. 1994 Apr;14(4):2391-403. doi: 10.1128/mcb.14.4.2391-2403.1994.
The yeast SLK1 (BCK1) gene encodes a mitogen-activated protein kinase (MAPK) activator protein which functions upstream in a protein kinase cascade that converges on the MAPK Slt2p (Mpk1p). Dominant alleles of SLK1 have been shown to bypass the conditional lethality of a protein kinase C mutation, pkc1-delta, suggesting that Pkc1p may regulate Slk1p function. Slk1p has an important role in morphogenesis and growth control, and deletions of the SLK1 gene are lethal in a spa2-delta mutant background. To search for genes that interact with the SLK1-SLT2 pathway, a synthetic lethal suppression screen was carried out. Genes which in multiple copies suppress the synthetic lethality of slk1-1 spa2-delta were identified, and one, the NHP6A gene, has been extensively characterized. The NHP6A gene and the closely related NHP6B gene were shown previously to encode HMG1-like chromatin-associated proteins. We demonstrate here that these genes are functionally redundant and that multiple copies of either NHP6A or NHP6B suppress slk1-delta and slt2-delta. Strains from which both NHP6 genes were deleted (nhp6-delta mutants) share many phenotypes with pkc1-delta, slk1-delta, and slt2-delta mutants. nhp6-delta cells display a temperature-sensitive growth defect that is rescued by the addition of 1 M sorbitol to the medium, and they are sensitive to starvation. nhp6-delta strains also exhibit a variety of morphological and cytoskeletal defects. At the restrictive temperature for growth, nhp6-delta mutant cells contain elongated buds and enlarged necks. Many cells have patches of chitin staining on their cell surfaces, and chitin deposition is enhanced at the necks of budded cells. nhp6-delta cells display a defect in actin polarity and often accumulate large actin chunks. Genetic and phenotypic analysis indicates that NHP6A and NHP6B function downstream of SLT2. Our results indicate that the Slt2p MAPK pathway in Saccharomyces cerevisiae may mediate its function in cell growth and morphogenesis, at least in part, through high-mobility group proteins.
酵母SLK1（BCK1）基因编码一种丝裂原活化蛋白激酶（MAPK）激活蛋白，该蛋白在汇聚于MAPK Slt2p（Mpk1p）的蛋白激酶级联反应中起上游作用。已证明SLK1的显性等位基因可绕过蛋白激酶C突变体pkc1 - delta的条件致死性，这表明Pkc1p可能调节Slk1p的功能。Slk1p在形态发生和生长控制中起重要作用，在spa2 - delta突变背景下，SLK1基因的缺失是致死的。为了寻找与SLK1 - SLT2途径相互作用的基因，进行了合成致死抑制筛选。鉴定出多个拷贝可抑制slk1 - 1 spa2 - delta合成致死性的基因，其中一个基因NHP6A已得到广泛研究。先前已表明NHP6A基因和密切相关的NHP6B基因编码类HMG1染色质相关蛋白。我们在此证明这些基因在功能上是冗余的，NHP6A或NHP6B的多个拷贝均可抑制slk1 - delta和slt2 - delta。两个NHP基因均被缺失的菌株（nhp6 - delta突变体）与pkc1 - delta、slk1 - delta和slt2 - delta突变体具有许多相同的表型。nhp6 - delta细胞表现出温度敏感的生长缺陷，向培养基中添加1 M山梨醇可挽救该缺陷，并且它们对饥饿敏感。nhp6 - delta菌株还表现出多种形态和细胞骨架缺陷。在生长的限制温度下，nhp6 - delta突变细胞含有细长的芽和增大的颈部。许多细胞在其细胞表面有几丁质染色斑块，并且在出芽细胞的颈部几丁质沉积增强。nhp6 - delta细胞在肌动蛋白极性方面存在缺陷，并且经常积累大的肌动蛋白块。遗传和表型分析表明NHP6A和NHP6B在SLT2的下游起作用。我们的结果表明，酿酒酵母中的Slt2p MAPK途径可能至少部分地通过高迁移率族蛋白介导其在细胞生长和形态发生中的功能。
