Pearce D A, Sherman F
Department of Biochemistry, University of Rochester School of Medicine and Dentistry, NY 14642, USA.
Proc Natl Acad Sci U S A. 1995 Apr 25;92(9):3735-9. doi: 10.1073/pnas.92.9.3735.
The level and structure of yeast iso-1-cytochrome c and iso-2-cytochrome c, encoded by the nuclear genes CYC1 and CYC7, respectively, are normally not altered in rho- mutants, which completely lack the cytochromes a.a3 subunits and cytochrome b that are encoded by mitochondrial DNA. In contrast, iso-cytochromes c containing the amino acid change Thr-78-->Ile (T78I) were observed at the normal or near-normal wild-type level in rho+ strains but were completely absent in rho- mutants. We have demonstrated with the "global" suppressor mutation Asn-52-->Ile and by pulse-chase labeling that the T78I iso-1-cytochrome c undergoes rapid cellular degradation in rho- mutants. Furthermore, specific mutations revealed that the deficiency of T78I iso-1 cytochrome c can be caused by the lack of cytochrome a.a3 or cytochrome c1, but not by the lack of cytochrome b. Thus, this and certain other, but not all, labile forms of cytochrome c are protected from degradation by the interaction with its physiological partners.
酵母同工酶-1-细胞色素c和同工酶-2-细胞色素c分别由核基因CYC1和CYC7编码，其水平和结构在rho-突变体中通常不会改变，rho-突变体完全缺乏由线粒体DNA编码的细胞色素a.a3亚基和细胞色素b。相比之下，含有氨基酸变化Thr-78→Ile（T78I）的同工酶细胞色素c在rho+菌株中以正常或接近正常的野生型水平被观察到，但在rho-突变体中则完全不存在。我们通过“全局”抑制突变Asn-52→Ile以及脉冲追踪标记证明，T78I同工酶-1-细胞色素c在rho-突变体中经历快速的细胞降解。此外，特定突变表明，T78I同工酶-1细胞色素c的缺乏可能是由于缺乏细胞色素a.a3或细胞色素c1，但不是由于缺乏细胞色素b。因此，这种以及某些其他但并非所有不稳定形式的细胞色素c通过与其生理伙伴的相互作用而免受降解。
