Laz T M, Pietras D F, Sherman F
Proc Natl Acad Sci U S A. 1984 Jul;81(14):4475-9. doi: 10.1073/pnas.81.14.4475.
The two unlinked genes CYC1 and CYC7 encode iso-1-cytochrome c and iso-2-cytochrome c, respectively, in the yeast Saccharomyces cerevisiae. An examination of the steady-state level of CYC1 and CYC7 mRNAs in normal and mutant strains grown under different conditions, along with previous results of apoprotein levels, demonstrate that CYC1 and CYC7 have similar and different modes of regulation. Both CYC1 and CYC7 mRNAs are diminished after anaerobic growth. In contrast, CYC1 mRNA but not CYC7 mRNA is decreased by heme deficiency in hem1 mutants. Although both CYC1 and CYC7 mRNAs are substantially lowered after growth in glucose medium, there is a difference in the kinetics of glucose derepression. CYC1 mRNA levels rise in the early logarithmic phase of growth before complete exhaustion of glucose, whereas CYC7 mRNA levels rise in the late logarithmic phase when the level of CYC1 mRNA has plateaued. For a brief period before cessation of growth, the level of CYC7 mRNA attains a level corresponding to the high derepressed level of CYC1 mRNA. The high amount of CYC7 mRNA is surprising because iso-2-cytochrome c constitutes only 5% of the total cytochrome c complement in derepressed cells. We suggest that iso-2-cytochrome c has the potential to comprise a major proportion of cytochrome c under certain physiologic conditions that have not been experimentally defined. The cyc3 mutant, which lacks the ability to attach heme groups to apocytochromes c, contains both CYC1 and CYC7 mRNAs in normal amounts. Yet, cyc3 mutants contain only apoiso-2-cytochrome c and not apoiso-1-cytochrome c. The lack of accumulation of apoiso-1-cytochrome c in cyc3 mutants, which contain CYC1 mRNA, suggests that apoiso-1-cytochrome c is extensively regulated by a post-transcriptional process.
在酿酒酵母中，两个不连锁的基因CYC1和CYC7分别编码同工型-1-细胞色素c和同工型-2-细胞色素c。对在不同条件下生长的正常菌株和突变菌株中CYC1和CYC7 mRNA的稳态水平进行检测，结合之前载脂蛋白水平的结果表明，CYC1和CYC7具有相似和不同的调控模式。厌氧生长后，CYC1和CYC7 mRNA均减少。相比之下，hem1突变体中血红素缺乏会导致CYC1 mRNA减少，但不会导致CYC7 mRNA减少。尽管在葡萄糖培养基中生长后，CYC1和CYC7 mRNA均大幅降低，但在葡萄糖去阻遏动力学方面存在差异。CYC1 mRNA水平在葡萄糖完全耗尽之前的生长对数早期阶段升高，而CYC7 mRNA水平在生长对数后期阶段升高，此时CYC1 mRNA水平已趋于平稳。在生长停止前的短时间内，CYC7 mRNA水平达到与CYC1 mRNA高度去阻遏水平相对应的水平。CYC7 mRNA的高含量令人惊讶，因为在去阻遏细胞中，同工型-2-细胞色素c仅占细胞色素c总量的5%。我们认为，在尚未通过实验确定的某些生理条件下，同工型-2-细胞色素c有可能构成细胞色素c的主要部分。cyc3突变体缺乏将血红素基团连接到脱辅基细胞色素c上的能力，其CYC1和CYC7 mRNA含量正常。然而，cyc3突变体仅含有脱辅基同工型-2-细胞色素c，而不含有脱辅基同工型-1-细胞色素c。在含有CYC1 mRNA的cyc3突变体中，脱辅基同工型-1-细胞色素c缺乏积累，这表明脱辅基同工型-1-细胞色素c受到转录后过程的广泛调控。
