Institut für Molekularbiologie II der Universität Zürich, Hönggerberg, CH-8093 Zürich, Switzerland.
EMBO J. 1982;1(1):27-33. doi: 10.1002/j.1460-2075.1982.tb01119.x.
DNA sequences of cloned histone coding sequences and spacers of sea urchin species that diverged long ago in evolution were compared. The highly repeated H4 and H3 genes active during early embryogenesis had evolved (in their silent sites) at a rate (0.5-0.6% base changes/Myr) similar to single-copy protein-coding genes and nearly as fast as spacer DNA (0.7% base changes/Myr) and unique DNA. Thus, evolution in the major histone genes conforms to a universal evolutionary clock based on the rate of base sequence change. By contrast, the H4 and H3 coding sequences and a non-transcribed spacer of the DNA clone h19 of Psammechinus miliaris show an exceptionally low rate of sequence evolution only 1/100 to 1/200 that predicted from the clock hypothesis. According to the classical model of gene inheritance, the h19 DNA sequences in the Psammechinus genome require unusual conservation mechanisms by selection at the level of the gene and spacer sequences. An alternative explanation could be recent horizontal gene transfer of a histone gene cluster from the very distantly related Strongylocentrotus dröbachiensis to the P. miliaris genome.
比较了在进化上早已分化的几种海胆物种的克隆组蛋白编码序列和间隔区的 DNA 序列。在早期胚胎发生过程中活跃的高度重复的 H4 和 H3 基因在沉默位点进化的速度（0.5-0.6%碱基变化/Myr）与单拷贝蛋白编码基因相似，几乎与间隔 DNA（0.7%碱基变化/Myr）和独特 DNA 一样快。因此，主要组蛋白基因的进化符合基于碱基序列变化率的普遍进化钟。相比之下，Psammechinus miliaris 的 DNA 克隆 h19 的 H4 和 H3 编码序列和一个非转录间隔区的序列进化速度异常缓慢，仅为从时钟假说预测的 1/100 到 1/200。根据经典的基因遗传模型，在 Psammechinus 基因组中，h19 DNA 序列需要通过基因和间隔序列的选择来进行特殊的保护机制。另一种解释可能是最近来自远缘的 Strongylocentrotus dröbachiensis 的组蛋白基因簇发生了水平基因转移到 P. miliaris 的基因组。
