COMPARISON OF RIBOSOMAL DNAS OF XENOPUS-LAEVIS AND XENOPUS-MULLERI - EVOLUTION OF TANDEM GENES
COMPARISON OF RIBOSOMAL DNAS OF XENOPUS-LAEVIS AND XENOPUS-MULLERI - EVOLUTION OF TANDEM GENES
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DOI：
10.1016/0022-2836(72)90521-9
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发表时间：
1972-01-01
影响因子：
5.6
通讯作者：
JORDAN, E
中科院分区：
文献类型：
--
作者：
BROWN, DD;WENSINK, PC;JORDAN, E
非洲爪哇和非洲爪哇的核糖体DNA在核苷酸序列上存在差异。碱基组成分别为67%和65%G+C。编码28 S和18 S核糖体核糖核酸的核苷酸序列不能根据大小、碱基组成或杂交保真度来区分。这两种核糖体DNA的区别在于它们的间隔区。从与异源rDNA杂交的间隔区转录的互补RNA不到与同源rDNA杂交的水平的20%，并通过电子显微镜下的变性图谱进一步比较了两种rDNA的部分变性分子。重复长度inx。MullerirDNA与INX大致相同。LaevisrDNA。而推测编码40 S核糖核酸前体的区域在X的核糖体DNA中具有非常相似的变性模式。LevisandX。Mulleri，间隔区的图案非常不同。理化和电子显微镜分析均表明，该重复序列为INX。多核糖体DNA在大小和核苷酸序列方面非常相似，如果不是完全相同的话，这一事实以前在X的rDNA中得到了证实。分布在18个S和28个S基因区之间的多个间隔区序列共同进化；18个S和28个S基因没有变化。虽然不同物种间的间隔区差异很大，但它们在每个物种内即使不完全相同，也非常相似。我们得出的结论是，一个间隔区序列中的突变必须以比这些基因发生新变化更快的速度传播到相邻的间隔区，这是一种“纠正”机制。这种发生在单个有机体内的现象被称为“水平”进化，与“垂直”进化不同，“垂直”进化是突变通过繁殖种群的传播。
The ribosomal DNA's ofXenopus laevisandXenopus mulleridiffer in their nucleotide sequences. Their base compositions are 67 and 65% G + C, respectively. The nucleotide sequences which code for 28 s and 18 s ribosomal RNA in the rDNA of the two species could not be distinguished by their size, base composition, or fidelity of hybridization. The difference between the two ribosomal DNA's lies in their spacer regions. Complementary RNA transcribed from spacer regions hybridized to heterologous rDNA at less than 20% of the level with which it hybridized to homologous rDNA.Partly denatured molecules of the two rDNA's were further compared by “denaturation mapping” in the electron microscope. The repeat length inX. mullerirDNA is about the same as that inX. laevisrDNA. While the regions presumed to code for the 40 s precursor of rRNA have very similar denaturation patterns in the ribosomal DNA ofX. laevisandX. mulleri, the patterns in the spacer regions are very different. Both physico-chemical and electron microscopic analyses show that the repeating sequences inX. mulleriribosomal DNA are very similar, if not identical, to each other with respect to size and nucleotide sequence, a fact previously demonstrated for the rDNA ofX. laevis.The multiple spacer sequences interspersed between the 18 s and 28 s gene regions have evolved together; the 18 s and 28 s genes have remained unchanged. Although the spacer regions differ greatly between species, they are very similar if not identical within each species. We conclude that a “correction” mechanism must operate to spread a mutation in one spacer sequence to the neighboring spacers faster than new changes arise in these genes. This phenomenon, which occurs within a single organism, is referred to as “horizontal” evolution, in contrast to “vertical” evolution which is the spread of a mutation through a breeding population.