Kunkel N S, Weinberg E S
Cell. 1978 Jun;14(2):313-26. doi: 10.1016/0092-8674(78)90117-4.
Two distinct populations of histone gene transcripts have been identified in the sea urchin embryo. Both late cleavage and mesenchyme blastula stages contain histone transcripts which hybridize to a full-length histone repeat recombinant DNA, pCO1. The histone RNAs of the two stages, however, are dissimilar in sequence. While the transcripts of the cleavage embryo form well matched hybrids with the plasmid DNA which are relatively resistant to RNAase, the hybrids containing the mesenchyme blastula transcripts melt some 10 degrees C lower and are twice as sensitive to RNAase. Hybridization of the two RNA samples to the Hha I fragments of the histone DNA, or to segments of the histone repeat subcloned in other plasmids, shows that many regions scattered along the repeat are complementary to widely diverged transcripts in the mesenchyme blastula RNA. The two RNA populations consist predominantly of polysomal RNA sequences and are most probably mRNAs for the five histones. The mesenchyme blastula RNA sequences in both S. purpuratus and L. pictus form hybrids with pCO1 DNA that are less stable than those containing L. pictus cleavage RNA, indicating the wide divergence of the two histone RNA populations. The bulk of the histone genes in S. purpuratus appear to be of the type coding for the early mRNAs. Only a small percentage of the several hundred gene copies are candidates for the type coding for the late mRNAs. The melting characteristics of the hybrids and the sensitivity of RNAase provide an assay for the late embryonic histone genes. Of the total RNA labeled during a 10 min pulse in the cleavage embryo, histone transcripts represent approximately 9.7 and 6.5% of the radioactivity in S. purpuratus and L. pictus, respectively. These values fall to 0.57 and 1.4%, respectively, at the mesenchyme blastula stage. Although histone genes are transcribed during these two periods, the type of gene which is active is switched at some point prior to the mesenchyme blastula stage.
在海胆胚胎中已鉴定出两种不同的组蛋白基因转录本群体。卵裂后期和间充质囊胚阶段都含有与全长组蛋白重复重组DNA（pCO1）杂交的组蛋白转录本。然而，这两个阶段的组蛋白RNA在序列上是不同的。卵裂胚胎的转录本与质粒DNA形成匹配良好的杂交体，这些杂交体对RNA酶相对抗性，而包含间充质囊胚转录本的杂交体在低约10摄氏度时解链，并且对RNA酶的敏感性是前者的两倍。将这两种RNA样品与组蛋白DNA的Hha I片段或亚克隆到其他质粒中的组蛋白重复片段进行杂交，结果表明，沿着重复序列散布的许多区域与间充质囊胚RNA中广泛不同的转录本互补。这两种RNA群体主要由多聚核糖体RNA序列组成，很可能是五种组蛋白的mRNA。紫球海胆（S. purpuratus）和花斑海胆（L. pictus）的间充质囊胚RNA序列与pCO1 DNA形成的杂交体比包含花斑海胆卵裂RNA的杂交体更不稳定，这表明这两种组蛋白RNA群体存在广泛差异。紫球海胆中的大部分组蛋白基因似乎是编码早期mRNA的类型。在数百个基因拷贝中，只有一小部分是编码晚期mRNA类型的候选基因。杂交体的解链特性和RNA酶的敏感性为晚期胚胎组蛋白基因提供了一种检测方法。在卵裂胚胎中10分钟脉冲标记期间的总RNA中，组蛋白转录本分别占紫球海胆和花斑海胆放射性的约9.7%和6.5%。在间充质囊胚阶段，这些值分别降至0.57%和1.4%。尽管组蛋白基因在这两个时期都有转录，但活跃的基因类型在间充质囊胚阶段之前的某个时间点发生了转换。
