Cohn R H, Kedes L H
Cell. 1979 Nov;18(3):855-64. doi: 10.1016/0092-8674(79)90137-5.
The linear arrangement and lengths of the spacers and coding regions in the two nonallelic histone gene variant clusters of L. pictus are remarkably homologous by R loop analysis and are similar in general topography to the histone gene repeat units of other sea urchins examined to date. No interventing sequences were detected. The coding regions of these two histone gene variants share considerable sequence homology; however, there are areas of nonhomology in every spacer region and the lengths of the nonhomologous spacers between the H2A and H1 genes are not the same for the two repeat unit classes (inter-gene heterogeneity). Combining length measurements obtained with both R loops and heteroduplexes suggests that the DNA sequences of the analogous leader regions for the two H1 mRNAs are nonhomologous. Similar observations were made for the H4 leader sequences, as well as the trailer region on H2B. S. purpuratus spacer DNA segments share little sequence homology with L. pictus; however, the analgous coding (and possibly flanking) regions have conserved their sequences. The various coding and spacer regions within a repeat unit do not share DNA sequences. Thus certain areas in the sea urchin histone gene repeat units have been highly conserved during evolution, while other areas have been allowed to undergo considerable sequence change not only between species but within a species.
通过R环分析可知，紫球海胆（L. pictus）两个非等位组蛋白基因变体簇中的间隔区和编码区的线性排列及长度具有显著的同源性，并且在总体拓扑结构上与迄今所研究的其他海胆的组蛋白基因重复单元相似。未检测到间隔序列。这两个组蛋白基因变体的编码区具有相当程度的序列同源性；然而，每个间隔区都存在非同源区域，并且对于这两类重复单元来说，H2A和H1基因之间非同源间隔区的长度并不相同（基因间异质性）。结合通过R环和异源双链体获得的长度测量结果表明，两种H1 mRNA类似前导区的DNA序列是非同源的。对于H4前导序列以及H2B上的尾随区也有类似的观察结果。紫海胆（S. purpuratus）的间隔区DNA片段与紫球海胆的序列同源性很低；然而，类似的编码（可能还有侧翼）区却保留了它们的序列。一个重复单元内的各种编码区和间隔区并不共享DNA序列。因此，海胆组蛋白基因重复单元中的某些区域在进化过程中高度保守，而其他区域不仅在物种之间，而且在一个物种内部都经历了相当大的序列变化。
