Analysis of the genes involved in the maintenance of mini-chromosomes in yeast.

含有自主复制序列（ARS）和着丝粒（CEN）的酵母质粒在酵母细胞中可以作为小染色体稳定地维持。我们选择了在高温下微染色体不稳定的突变体并检测了这些表型。我们这个项目的目标是定义基因产物如何进行复制或分裂。利用Hartwell等人开发的系统，我们新选择了3个ts突变体；两个突变体形成了带有白色扇区的粉红色菌落（可能是复制缺陷），一个形成了带有白色和红色扇区的粉红色菌落（非分离？）现在我们正试图克隆这些基因，通过补充ts表现型的活性。GSTl基因影响小染色体的稳定性，是gls向s转化的关键基因。微染色体在34ºC时不稳定且容易丢失。与26‰比较。基因产物(MW。77K)与多肽链延伸因子有同源结构域。该基因与框架移位抑制因子SUFl2、全能抑制因子sup2 （sup36）和同种异体抑制因子sal3相同。我们正在研究这种蛋白质的功能。我们还从人成纤维细胞cDNA文库中克隆了酵母GSTl基因的人同源物。该基因编码的蛋白比酵母GSTl小，但包含与EFlalpha同源的完整结构域和gtp结合蛋白的一致序列。人GSTl基因在进入s期前mRNA表达量最大。

Yeast plasmids containing the autonomously replicating sequence(ARS) and the centromere (CEN) can be maintained rather stably as mini- chromosomes in yeast cells. We selected the mutants in which mini- chromosomes were unstable at a higher temperature and examined those phenotypes. Our goal of this project is to define how the gene products function for either replication or partitioning.By using the system developed by Hartwell et al., we newly selected three ts mutants; two mutants formed pink colonies with white sectors (presumably defective in replication), one formed pink colonies with white and red sectors (non-disjunction ?). Now we are trying to clone the genes, by complementing activity of the ts phenotype.The GSTl gene which is essential for Gl-to-S transition, affects the stability of mini-chromosomes. The mini-chromosomes were unstable and easily lost at 34ﾟC. compared at 26ﾟC. The gene product (MW. 77K) has a homologous domain to polypeptide chain elongation factor lalpha. This gene was found to be the same as the frame-shift suppressor SUFl2, omnipotent suppressor sup2 (sup36) and allosuppressor sal3. We are in progress in studying the function of this protein.We also cloned the human homologue of the yeast GSTl gene from cDNA library of human fibroblast. The gene coded for a protein smaller than yeast GSTl but contained the complete domain homologous to EFlalpha and the consensus sequence for GTP-binding proteins. The mRNA level of the human GSTl gene was the maximum just before entering the S-phase.