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

1.编码大肠杆菌肽链释放因子3的prfC基因的鉴定：细菌中蛋白质合成的终止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RF-3刺激RF-1和RF-2活性，最初在大肠杆菌中鉴定，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，我们通过随机插入突变选择了新的无义抑制突变。其中一个突变被命名为tos-1，定位于E.大肠杆菌染色体上，并抑制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 Da的蛋白质。提取物含有过度生产的Tos蛋白显着增加核糖体终止复合物的形成，并刺激RF-1或RF-2的活性，在密码子依赖性的体外终止试验。这些结果完全符合 ...更多信息 e在关于RF-3的原始出版物中描述，因此tos基因被命名为prfC. 2。大肠杆菌赖氨酰-tRNA合成酶的调控与功能大肠杆菌：多样性和协调：在大肠杆菌中，赖氨酰-tRNA合成酶由两个不同的基因lysS（组成型）和lysU（诱导型）合成，但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一个重要的控制机制lysU的表达，这涉及到亮氨酸响应调节蛋白（Lrp）和翻译增强元件称为“下游框”。次要精氨酸（AGG）tRNA对酿酒酵母Ty 1转座和线粒体热休克蛋白表达的调控：酿酒酵母反转录转座子Ty 1基因组含有TYA 1（gag）和TYB 1（pol）两个基因，并且TYA 1-TYB 1融合蛋白是通过在TYA 1序列CUU AGG C中进行+1核糖体移码而合成的。移码需要核糖体在罕见的AGG-精氨酸密码子处暂停和亮氨酰-tRNA从CUU到UUA的滑动。破坏tRNA（CCU）基因，命名为HSX 1，导致翻译移码增加和逆转录转座减少。HSX 1基因的破坏也导致了SSC 1基因的热休克诱导缺陷，该基因编码S.啤酒。由于hsx 1突变不影响其他热休克蛋白基因的表达，SSC 1的表达可能是由一种新的机制，涉及小tRNA（CCU）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