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Abstract：
tDNA sequences essential for promotion of transcription have been identified for a tRNA1met gene of X. laevis. A cloned tRNA gene unit was altered by resection of the 5\' flanking sequences or by specific deletions of gene and trailing sequences. Gene internal sequences were also substituted by unrelated sequences. The gene units mutated in this way were coinjected into the oocyte together with cloned X. laevis 5S DNA, or were transcribed in vitro, in order to assess the effects of the sequence manipulation on transcription. We find major control sequences to be located near the 5\' and the 3\' ends of the sequences coding for the mature tRNA. A first such control sequence, having profound effects on the rate of tRNA production, has been mapped to sequence position 8-13 within the structural gene. A second regulatory sequence occurs within the region 51 to 72, that is, in or near the sequence coding for the pseudouridine loop of the tRNA. The sequences pinpointed in this way coincide with highly conserved sequences found in most, if not all, eucaryotic tRNAs. The anterior and the posterior control elements can be moved apart from one another without affecting the rate or points ot initiation and termination of transcription. While all deletions within the sequence coding for the mature tRNA led to inactivity of the mutated genes, substitution of the central portion by concatenated Hind III linkers produced gene units active in transcription. We postulate that the middle portion of the gene has a function in keeping the two control elements at sequence positions 8-30 and 51-72 at a critical distance from one another, a distance that can be enlarged but not shortened without obliterating the activity of the gene.
摘要：
对于X.laevis的tRNA1met基因,已经鉴定了促进转录所必需的tDNA序列。通过切除5'侧翼序列或通过基因和拖尾序列的特异性缺失来改变克隆的tRNA基因单位。基因内部序列也被不相关的序列取代。以这种方式突变的基因单元与克隆的X.laevis5SDNA一起被共同注射到卵母细胞中，或者在体外转录，以评估序列操作对转录的影响。我们发现主要控制序列位于编码成熟tRNA的序列的5'和3'末端附近。第一个这样的控制序列，对tRNA的生产率有深远的影响，已定位到结构基因内的序列位置8-13。第二调节序列出现在区域51至72内,即,在编码tRNA的假尿苷环的序列中或附近。以这种方式确定的序列与大多数发现的高度保守序列一致，如果不是全部,真核tRNA。前控制元件和后控制元件可以彼此分开,而不影响转录起始和终止的速率或点。虽然编码成熟tRNA的序列中的所有缺失都导致突变基因的失活，通过串联的HindIII接头取代中心部分产生转录活跃的基因单位。我们推测，基因的中间部分具有使序列位置8-30和51-72的两个控制元件彼此保持临界距离的功能，在不消除基因活性的情况下可以扩大但不能缩短的距离。
