Kim K S, Rosenkrantz M S, Guarente L
Mol Cell Biol. 1986 Jun;6(6):1936-42. doi: 10.1128/mcb.6.6.1936-1942.1986.
The tricarboxylic acid cycle occurs within the mitochondria of the yeast Saccharomyces cerevisiae. A nuclear gene encoding the tricarboxylic acid cycle enzyme citrate synthase has previously been isolated (M. Suissa, K. Suda, and G. Schatz, EMBO J. 3:1773-1781, 1984) and is referred to here as CIT1. We report here the isolation, by an immunological method, of a second nuclear gene encoding citrate synthase (CIT2). Disruption of both genes in the yeast genome was necessary to produce classical citrate synthase-deficient phenotypes: glutamate auxotrophy and poor growth on rich medium containing lactate, a nonfermentable carbon source. Therefore, the citrate synthase produced from either gene was sufficient for these metabolic roles. Transcription of both genes was maximally repressed in medium containing both glucose and glutamate. However, transcription of CIT1 but not of CIT2 was derepressed in medium containing a nonfermentable carbon source. The significance of the presence of two genes encoding citrate synthase in S. cerevisiae is discussed.
三羧酸循环发生在酿酒酵母的线粒体中。之前已分离出一个编码三羧酸循环酶柠檬酸合酶的核基因（M. 苏伊萨、K. 须田和G. 沙茨，《欧洲分子生物学组织杂志》3:1773 - 1781, 1984），本文中称之为CIT1。我们在此报告通过免疫学方法分离出的另一个编码柠檬酸合酶的核基因（CIT2）。要产生典型的柠檬酸合酶缺陷型表型，即谷氨酸营养缺陷型以及在含有乳酸（一种不可发酵碳源）的丰富培养基上生长不良，有必要破坏酵母基因组中的这两个基因。因此，由任一基因产生的柠檬酸合酶对于这些代谢功能来说都是足够的。在同时含有葡萄糖和谷氨酸的培养基中，这两个基因的转录均受到最大程度的抑制。然而，在含有不可发酵碳源的培养基中，CIT1的转录而非CIT2的转录被解除抑制。本文讨论了酿酒酵母中存在两个编码柠檬酸合酶基因的意义。
