Harlow P, Litwin S, Nemer M
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
J Mol Evol. 1988;27(1):56-64. doi: 10.1007/BF02099730.
Sea urchin and rodent genomes have been posited to evolve rapidly as indicated by divergences in single copy nuclear DNA sequences. We have examined whether the synonymous substitution rates of three highly conserved genes, beta-tubulin, histone H4, and histone H3, adhere to these high genomic substitution rates by comparing sequences between two sea urchins, Strongylocentrotus purpuratus and Lytechinus pictus, and between rodents and humans. Whereas the rate of change between the 3' untranslated regions of the beta-tubulin cDNA of S. purpuratus (Sp-beta 1), sequenced in this study, and of L. pictus (Lp-beta 3) was consistent with the overall rate of change estimated from previous DNA hybridization results between these species, the synonymous substitution rates for the carboxyl domains of these beta-tubulins, as well as for the late histones H4 and H3, were significantly depressed. In contrast, synonymous nucleotide substitution rates between rodents and between rodent and human for the carboxyl domain proper of identical beta-tubulin isotypes and for histone H4 and H3.1 did not differ from the overall rate of change for the rodent genomes. Moreover, an analysis of paralogous human and mouse beta-tubulin sequences supported the conclusion that the synonymous substitution rates in the mouse were higher than those in the human. Differences in constraint on evolutionary change were not evident strictly from the conserved amino acid sequences and base compositions of these genes. Other constraining influences seemed more relevant to the departure of the synonymous substitution rates of the sea urchin beta-tubulin and histone coding regions from the average genomic rate.
海胆和啮齿动物的基因组被认为进化迅速，单拷贝核DNA序列的差异表明了这一点。我们通过比较两种海胆（紫球海胆和花斑海胆）之间以及啮齿动物和人类之间的序列，研究了三个高度保守基因（β-微管蛋白、组蛋白H4和组蛋白H3）的同义替换率是否符合这些高基因组替换率。本研究中测序的紫球海胆（Sp-β1）和花斑海胆（Lp-β3）的β-微管蛋白cDNA的3'非翻译区之间的变化率与根据这些物种先前的DNA杂交结果估计的总体变化率一致，然而，这些β-微管蛋白的羧基结构域以及晚期组蛋白H4和H3的同义替换率却显著降低。相比之下，相同β-微管蛋白亚型的羧基结构域以及组蛋白H4和H3.1在啮齿动物之间以及啮齿动物与人类之间的同义核苷酸替换率与啮齿动物基因组的总体变化率没有差异。此外，对人源和鼠源β-微管蛋白旁系同源序列的分析支持了小鼠的同义替换率高于人类的结论。从这些基因保守的氨基酸序列和碱基组成来看，进化变化限制方面的差异并不明显。其他限制因素似乎与海胆β-微管蛋白和组蛋白编码区的同义替换率偏离基因组平均速率的情况更为相关。
