Mitchelson K, Moss T
Biophysics Laboratories, Portsmouth Polytechnic, UK.
Nucleic Acids Res. 1987 Nov 25;15(22):9577-96. doi: 10.1093/nar/15.22.9577.
It has been suggested that the tandemly repeated ribosomal genes of eukaryotes may be subject to a special mechanism of transcriptional enhancement, called Readthrough Enhancement, in which transcription factors are recycled. Recent experiments with the mouse ribosomal genes, although consistent with this possibility, were unable to distinguish between true Readthrough Enhancement and promoter occlusion. To test directly for Readthrough Enhancement, the pre-ribosomal RNA of Xenopus laevis was prematurely terminated within the 18S gene on a circular template. This premature termination was found to reduce the efficiency of pre-ribosomal RNA promotion in cis by 80 to 90%. Since the pre-ribosomal RNA is normally terminated only 213 base pairs upstream of its own initiation site, the results strongly suggest that the recycling of RNA polymerase, or Readthrough Enhancement, is a means by which ribosomal transcription is enhanced in Xenopus laevis.
有人提出,真核生物串联重复的核糖体基因可能受到一种特殊的转录增强机制的影响,称为通读增强,其中转录因子会循环利用。最近对小鼠核糖体基因进行的实验,尽管与这种可能性相符,但无法区分真正的通读增强和启动子封闭。为了直接测试通读增强,非洲爪蟾的前核糖体RNA在环状模板上的18S基因内被提前终止。发现这种提前终止会使顺式作用下的前核糖体RNA启动效率降低80%至90%。由于前核糖体RNA通常仅在其自身起始位点上游213个碱基对处终止,这些结果强烈表明,RNA聚合酶的循环利用,即通读增强,是非洲爪蟾核糖体转录增强的一种方式。