Reyes V M, Newman A, Abelson J
Mol Cell Biol. 1986 Jul;6(7):2436-42. doi: 10.1128/mcb.6.7.2436-2442.1986.
tRNA genes occur in the yeast genome as highly dispersed and independent transcriptional units. The 5'-tRNAArg-tRNAAsp-3' gene tandem, separated by a 10-base-pair spacer sequence, thus represents a rare case of tight clustering. Previous in vitro studies did not reveal any primary transcript from the tRNAAsp gene, but rather a dimeric precursor containing both gene sequences plus spacer, which undergoes a series of maturation steps. This seems anomalous since the tRNAAsp gene contains the sequences necessary for its own transcription. We found that site-directed mutation of the highly conserved C at position 56 to a G in the tRNAArg gene suppresses all transcription and does not activate the tRNAAsp gene. Precise deletion of the entire tRNAArg gene gives a similar result. Rescue of tRNAAsp gene transcription is effected either by the precise deletion of both the tRNAArg gene and spacer or by the precise deletion of this gene with concomitant introduction of an artificial RNA polymerase III start site in the spacer. This artificial start site is ineffective if the tRNAArg gene is present upstream.
tRNA基因在酵母基因组中以高度分散且独立的转录单位形式存在。由10个碱基对的间隔序列隔开的“5'-tRNA精氨酸-tRNA天冬氨酸-3'”基因串联体，因此代表了紧密成簇的罕见情况。先前的体外研究未揭示tRNA天冬氨酸基因的任何初级转录本，而是发现了一种包含两个基因序列加间隔区的二聚体前体，该前体经历一系列成熟步骤。这似乎不合常理，因为tRNA天冬氨酸基因包含自身转录所需的序列。我们发现，将tRNA精氨酸基因中第56位高度保守的C定点突变为G会抑制所有转录，且不会激活tRNA天冬氨酸基因。精确删除整个tRNA精氨酸基因会得到类似结果。通过精确删除tRNA精氨酸基因和间隔区，或者通过精确删除该基因并在间隔区引入人工RNA聚合酶III起始位点，可实现tRNA天冬氨酸基因转录的拯救。如果tRNA精氨酸基因位于上游，这个人工起始位点则无效。
