Post-Transcriptional Control of Gene Expression : mRNA Degradation and Translational Regulation

1. 大肠杆菌肽链释放因子3编码prfC基因的鉴定：终止细菌蛋白质合成需要两个密码子特异性多肽释放因子RF-1和RF-2。第三种因子，刺激RF-1和RF-2活性的RF-3，最初是在大肠杆菌中发现的，但自20世纪70年代以来很少受到关注。为了寻找编码RF-3的基因，我们采用随机插入诱变的方法选择了新的无义抑制突变。其中一个名为tos-1的突变定位于大肠杆菌染色体上的99.2 min区域，并抑制了所有三个终止密码子。DNA和蛋白质序列的互补研究和分析表明，tos基因编码59,442个Da蛋白。在密码子依赖的体外终止实验中，含有过量生成的Tos蛋白的提取物显著增加核糖体终止复合物的形成，并刺激RF-1或RF-2的活性。这些结果与RF-3的原始出版物中描述的结果完全吻合，因此tos基因被指定为prfc。大肠杆菌中赖氨酸- trna合成酶的调控与功能：多样性与协调性：在大肠杆菌中，赖氨酸- trna合成酶是由两个不同的基因lysS（组成型）和lysU（诱导型）合成的，然而，这两个基因的生理意义和差异调控机制一直是一个谜。我们已经成功地发现了lysU表达的重要控制机制，该机制涉及亮氨酸响应性调节蛋白（Lrp）和称为“下游盒”的翻译增强子元件。酿酒酵母（Saccharomyces cerevisiae）中minor arginine (AGG) tRNA对Ty1转位和线粒体热休克蛋白表达的调控：酿酒酵母（Saccharomyces cerevisiae）逆转录转座子Ty1基因组包含两个基因，TYA1 （gag）和TYB1 （pol）基因，TYA1-TYB1融合蛋白是通过TYA1序列CUU AGG c +1核糖体移框合成的。tRNA（CCU）基因HSX1的破坏导致翻译移框增加和反转录转位减少。HSX1基因的破坏还导致SSC1基因的热休克诱导缺陷，该基因编码酿酒葡萄球菌的线粒体伴侣蛋白hsp70。由于hsx1突变不影响其他hsp基因的表达，SSC1的表达可能受到一种涉及次要tRNA （CCU）的新机制的控制。少

1. Identification of the prfC gene encoding peptide-chain-release factor 3 of Escherichia coli : The termination of protein synthesis in bacteria requires two codon-specific polypeptide release factors, RF-1 and RF-2. A third factor, RF-3, that stimulates the RF-1 and RF-2 activities, was originally identified in E.coli, but it has received little attention since the 1970's. To search for the gene encoding RF-3, we selected novel nonsense-suppressor mutations by random insertion mutagenesis. One of these mutations, named tos-1, mapped to the 99.2 min region on the E. coli chromosome and suppressed all three stop codons. Complementation studies and analyses of the DNA and protein sequences revealed that the tos gene encodes a 59,442 Da protein. Extracts containing the overproduced Tos protein markedly increased the formation of ribosomal termination complexes and stimulated the RF-1 or RF-2 activity in the codon-dependent in vitro termination assay. These results fit perfectly with thos … More e described in the original publications on RF-3 and the tos gene has therefore been designated prfC.2. Control and function of lysyl-tRNA synthetases in E. coli : diversity and co-ordination : Lysyl-tRNA synthetases are synthesized from two distinct genes in E.coli, lysS (constitutively) and lysU (inducibly), however, the physiological significance and the differential control mechanism of these two genes have been a long-standing puzzle. We have successfully uncovered a significant control mechanism of lysU expression, that involves the leucine-responsive regulatory protein (Lrp) and a translational enhancer element called "downstream box".3. Regulation of Ty1 transposition and mitochondrial heat shock protein expression by the minor arginine (AGG) tRNA in Saccharomyces cerevisiae : The S. cerevisiae retrotransposon Ty1 genome contains two genes, TYA1 (gag) and TYB1 (pol) genes, and the TYA1-TYB1 fusion protein is synthesized by +1 ribosomal frameshifting in the TYA1 sequence CUU AGG C. Ribosomal pausing at a rare AGG-arginine codon and slippage of a leucyl-tRNA from CUU to UUA are required for frameshifting. Disruption of the tRNA(CCU) gene, designated HSX1, caused increased translational frameshifting and decreased retrotransposition. Disruption of the HSX1 gene also caused a defect in heat-shock induction of the SSC1 gene which encodes a mitochondrial chaperon, hsp70, of S. cerevisiae. Since the hsx1 mutation did not affect expression of other hsp genes, SSC1 expression is likely controlled by a novel mechanism involving the minor tRNA (CCU). Less