Zhang S, Rydén-Aulin M, Isaksson L A
Department of Microbiology Stockholm University, Sweden.
J Mol Biol. 1996 Aug 16;261(2):98-107. doi: 10.1006/jmbi.1996.0444.
Translation termination at UAG is influenced by the nature of the 5' flanking codon in Escherichia coli. Readthrough of the stop codon is always higher in a strain with mutant (prfA1) as compared to wild-type (prfA+) release factor one (RF1). Isocodons, which differ in the last base and are decoded by the same tRNA species, affect termination at UAG differently in strains with mutant or wild-type RF1. No general preference of the last codon base to favour readthrough or termination can be found. The data suggest that RF1 is sensitive to the nature of the wobble base anticodon-codon interaction at the ribosomal peptidyl-tRNA binding site (P-site). For some isoaccepting P-site tRNAs (tRNA3(Pro) versus tRNA2(Pro), tRNA4(Thr) versus tRNA1,3Thr) the effect is different on mutant and wild-type RF1, suggesting an interaction between RF1 at the aminoacyl-tRNA acceptor site (A-site) and the P-site tRNA itself. The glycine codons GGA (tRNA2(Gly)) and GGG (tRNA2,3(Gly)) at the ribosomal P-site are associated with an almost threefold higher readthrough of UAG than any of the other 42 codons tested, including the glycine codons GGU/C, in a strain with wild-type RF1. This differential response to the glycine codons is lost in the strain with the mutant form of RF1 since readthrough is increased to a similar high level for all four glycine codons. High alpha-helix propensity of the last amino acid residue at the C-terminal end of the nascent peptide is correlated with an increased termination at UAG. The effect is stronger on mutant compared to wild-type RF1. The data suggest that RF1-mediated termination at UAG is sensitive to the nature of the codon-anticodon interaction of the wobble base, the last amino acid residue of the nascent peptide chain, and the tRNA at the ribosomal P-site.
在大肠杆菌中，UAG处的翻译终止受5'侧翼密码子性质的影响。与野生型（prfA +）释放因子1（RF1）相比，具有突变型（prfA1）的菌株中终止密码子的通读率总是更高。在最后一个碱基上不同且由相同tRNA种类解码的同功密码子，在具有突变型或野生型RF1的菌株中对UAG处的终止有不同影响。找不到最后一个密码子碱基对通读或终止的一般偏好。数据表明，RF1对核糖体肽基 - tRNA结合位点（P位点）处摆动碱基反密码子 - 密码子相互作用的性质敏感。对于一些同功接受P位点tRNA（tRNA3（Pro）与tRNA2（Pro），tRNA4（Thr）与tRNA1,3Thr），对突变型和野生型RF1的影响不同，表明RF1在氨酰 - tRNA受体位点（A位点）与P位点tRNA本身之间存在相互作用。在具有野生型RF1的菌株中，核糖体P位点处的甘氨酸密码子GGA（tRNA2（Gly））和GGG（tRNA2,3（Gly））与UAG的通读率几乎比测试的其他42个密码子中的任何一个高近三倍，包括甘氨酸密码子GGU / C。在具有突变型RF1的菌株中，对甘氨酸密码子的这种差异反应消失了，因为所有四个甘氨酸密码子的通读率都增加到了相似的高水平。新生肽C末端最后一个氨基酸残基的高α-螺旋倾向与UAG处终止增加相关。与野生型RF1相比，对突变型的影响更强。数据表明，RF1介导的UAG处终止对摆动碱基的密码子 - 反密码子相互作用、新生肽链的最后一个氨基酸残基以及核糖体P位点处的tRNA的性质敏感。
