Crane-Robinson C
Biophysics Laboratories, University of Portsmouth, UK.
Bioessays. 1999 May;21(5):367-71. doi: 10.1002/(SICI)1521-1878(199905)21:5<367::AID-BIES2>3.0.CO;2-4.
In developing Xenopus laevis embryos the multiple-copy oocyte-type 5S RNA genes are progressively shut down. Results presented in three recent articles 1-3 together demonstrate that replacement of the cleavage stage linker histone B4 by somatic H1 leads to chromatosomes positioned directly over these genes and adjacent sequences so as to occlude the binding site for the critical transcription factor TFIIIA. In contrast, on the somatic-type 5S genes the somatic H1 positions chromatosomes about 65 bp further upstream, thereby leaving the TFIIIA binding site exposed and the genes active. The somatic linker histone thus functions as a specific gene repressor.
在非洲爪蟾胚胎发育过程中，多拷贝的卵母细胞型5S RNA基因会逐渐关闭。最近三篇文章1 - 3中呈现的结果共同表明，体细胞型H1取代卵裂期连接组蛋白B4会导致核小体定位在这些基因及相邻序列的正上方，从而封闭关键转录因子TFIIIA的结合位点。相比之下，在体细胞型5S基因上，体细胞型H1使核小体定位在上游约65 bp处，从而使TFIIIA结合位点暴露，基因保持活跃。因此，体细胞连接组蛋白起到了特异性基因阻遏物的作用。
