Gaut B S, Muse S V, Clegg M T
Department of Botany and Plant Sciences, University of California, Riverside 92521.
Mol Phylogenet Evol. 1993 Jun;2(2):89-96. doi: 10.1006/mpev.1993.1009.
Coding sequences from maize, rice, tobacco, and liverwort chloroplasts are aligned and subjected to relative rate tests. Results of rate tests suggest that coding sequences from maize and rice are evolving with homogeneous rates of nucleotide substitution while coding sequences from the grass lineages (i.e., maize and rice) are evolving at a faster rate than coding sequences from the tobacco chloroplast. Rate tests also suggest that particular loci evolve at significantly faster rates in grass chloroplast genomes than the tobacco chloroplast genome. These loci encode proteins important to RNA polymerase, the H(+)-ATPase complex, and the ribosomal proteins. Much of the variation at these loci can be attributed to differences in nonsynonymous substitution rates. Taken together, these studies suggest that the chloroplast DNA molecular clock varies both between evolutionary lineages and between protein coding loci.
对玉米、水稻、烟草和地钱叶绿体的编码序列进行比对，并进行相对速率测试。速率测试结果表明，玉米和水稻的编码序列以均匀的核苷酸替代速率进化，而禾本科谱系（即玉米和水稻）的编码序列进化速率比烟草叶绿体的编码序列快。速率测试还表明，禾本科叶绿体基因组中的特定基因座进化速率明显快于烟草叶绿体基因组。这些基因座编码对RNA聚合酶、H(+)-ATP酶复合体和核糖体蛋白重要的蛋白质。这些基因座的大部分变异可归因于非同义替代率的差异。综合来看，这些研究表明叶绿体DNA分子钟在进化谱系之间以及蛋白质编码基因座之间都有所不同。
