Conde M F, Boynton J E, Gillham N W, Harris E H, Tingle C L, Wang W L
Mol Gen Genet. 1975 Oct 3;140(3):183-220. doi: 10.1007/BF00334266.
Six chloroplast gene mutants of Chlamydomonas reinhardtii resistant to spectinomycin, erythromycin, or streptomycin have been assessed for antibiotic resistance of their chloroplast ribosomes. Four of these mutations clearly confer high levels of antibiotic resistance on the chloroplast ribosomes both in vivo. Although one mutant resistant to streptomycin and one resistant to spectinomycin have chloroplast ribosomes as sensitive to antibiotics as those of wild type in vivo, these mutations can be shown to alter the wildtype sensitivity of chloroplast ribosomes in polynucleotide-directed amino acid incorporation in vitro. Genetic analysis of these six chloroplast mutants and three similar mutants (Sager, 1972), two of which have been shown to affect chloroplast ribosomes (Mets and Bogorad, 1972; Schlanger and Sager, 1974), indicates that in Chlamydomonas at least three chloroplast gene loci can affect streptomycin resistance of chloroplast ribosomes and that two can affect erythromycin resistance. The three spectinomycin-resistant mutants examined appear to be alleles at a single chloroplast gene locus, but may represent mutations at two different sites within the same gene. Unlike wild type, the streptomycin and spectinomycin resistant mutants which have chloroplast ribosomes sensitive to antibiotics in vivo, grow well in the presence of antibiotic by respiring exogenously supplied acetate as a carbon source, and have normal levels of cytochrome oxidase activity and cyanide-sensitive respiration. We conclude that mitochondrial protein synthesis in these mutants is resistant to these antibiotics, whereas in wild type it is sensitive. To explain the behavior of these two chloroplast gene mutants as well as other one-step mutants which are resistant both photosynthetically and when respiring acetate in the dark, we have postulated that a mutation in a single chloroplast gene may result in alteration of both chloroplast and mitochondrial ribosomes. Mitochondrial resistance would appear to be the minimal necessary condition for survival of all such mutants, and antibiotic-resistant chloroplast ribosomes would be necessary for survival only under photosynthetic conditions.
已对莱茵衣藻的六个对壮观霉素、红霉素或链霉素具有抗性的叶绿体基因突变体的叶绿体核糖体进行了抗生素抗性评估。其中四个突变在体内均能使叶绿体核糖体产生高水平的抗生素抗性。尽管一个对链霉素具有抗性的突变体和一个对壮观霉素具有抗性的突变体在体内其叶绿体核糖体对抗生素的敏感性与野生型相同，但在体外多核苷酸指导的氨基酸掺入实验中，这些突变可改变叶绿体核糖体的野生型敏感性。对这六个叶绿体突变体和三个类似突变体（Sager，1972）进行的遗传分析表明，在衣藻中，至少有三个叶绿体基因位点可影响叶绿体核糖体对链霉素的抗性，两个基因位点可影响对红霉素的抗性。所检测的三个对壮观霉素具有抗性的突变体似乎是位于单个叶绿体基因位点的等位基因，但可能代表同一基因内两个不同位点的突变。与野生型不同，那些在体内叶绿体核糖体对抗生素敏感的链霉素和壮观霉素抗性突变体，通过以外源供应的乙酸盐作为碳源进行呼吸作用，在抗生素存在的情况下生长良好，并且具有正常水平的细胞色素氧化酶活性和对氰化物敏感的呼吸作用。我们得出结论，这些突变体中的线粒体蛋白质合成对这些抗生素具有抗性，而野生型则敏感。为了解释这两个叶绿体基因突变体以及其他在光合作用和黑暗中以乙酸盐呼吸时均具有抗性的一步突变体的行为，我们推测单个叶绿体基因的突变可能导致叶绿体和线粒体核糖体均发生改变。线粒体抗性似乎是所有此类突变体存活的最低必要条件，而抗生素抗性叶绿体核糖体仅在光合条件下才是存活所必需的。
