Brown C M, Stockwell P A, Trotman C N, Tate W P
Department of Biochemistry, University of Otago, Dunedin, New Zealand.
Nucleic Acids Res. 1990 Apr 25;18(8):2079-86. doi: 10.1093/nar/18.8.2079.
The sequences around the stop codons of 862 Escherichia coli genes have been analysed to identify any additional features which contribute to the signal for the termination of protein synthesis. Highly significant deviations from the expected nucleotide distribution were observed, both before and after the stop codon. Immediately prior to UAA stop codons in E. coli there is a preference for codons of the form NAR (any base, adenine, purine), and in particular those that code for glutamine or the basic amino acids. In contrast, codons for threonine or branched nonpolar amino acids were under-represented. Uridine was over-represented in the nucleotide position immediately following all three stop codons, whereas adenine and cytosine were under-represented. This pattern is accentuated in highly expressed genes, but is not as marked in either lowly expressed genes or those that terminate in UAG, the codon specifically recognised by polypeptide chain release factor-1. These observations suggest that for the efficient termination of protein synthesis in E. coli, the 'stop signal' may be a tetranucleotide, rather than simply a tri-nucleotide codon, and that polypeptide chain release factor-2 recognises this extended signal. The sequence following stop codons was analysed in genes from several other procaryotes and bacteriophages. Salmonella typhimurium, Bacillus subtilis, bacteriophages and the methanogenic archaebacteria showed a similar bias to E. coli.
对862个大肠杆菌基因终止密码子周围的序列进行了分析，以确定有助于蛋白质合成终止信号的任何其他特征。在终止密码子之前和之后都观察到与预期核苷酸分布的高度显著偏差。在大肠杆菌中，紧接UAA终止密码子之前，偏好NAR（任何碱基、腺嘌呤、嘌呤）形式的密码子，特别是那些编码谷氨酰胺或碱性氨基酸的密码子。相比之下，苏氨酸或支链非极性氨基酸的密码子则代表性不足。在所有三个终止密码子之后的核苷酸位置，尿苷的含量过高，而腺嘌呤和胞嘧啶的含量则过低。这种模式在高表达基因中更为明显，但在低表达基因或那些以UAG（多肽链释放因子-1特异性识别的密码子）终止的基因中则不那么明显。这些观察结果表明，对于大肠杆菌中蛋白质合成的有效终止，“终止信号”可能是一个四核苷酸，而不仅仅是一个三核苷酸密码子，并且多肽链释放因子-2识别这个扩展信号。对其他几种原核生物和噬菌体基因中的终止密码子之后的序列进行了分析。鼠伤寒沙门氏菌、枯草芽孢杆菌、噬菌体和产甲烷古细菌显示出与大肠杆菌类似的偏向性。
