Lim Valery I, Garber Maria B
Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Vavilov str. 32, 119991 Moscow, Russian Federation.
J Mol Biol. 2005 Feb 18;346(2):395-8. doi: 10.1016/j.jmb.2004.11.061. Epub 2004 Dec 19.
Bacterial ribosomes stalled on defective mRNAs are rescued by tmRNA that functions as both tRNA and mRNA. The first ribosomal elongation cycle on tmRNA where tmRNA functions as tRNA is highly unusual: occupation of the ribosomal A site by tmRNA occurs without codon:anticodon pairing. Our analysis shows that in this case the role of a codon:anticodon duplex should be accomplished by a single unpaired triplet. In order that tmRNA could participate in the ribosomal elongation cycle, a triplet preceding the mRNA portion of tmRNA (the -1triplet) should be in the A-form and this form should be recognized by the ribosomal decoding center. A rule is derived that determines what triplets cannot be used as the -1triplet. The rule was tested with the -1triplets of all known 414 tmRNA species. All 23 observed -1triplets follow the formulated rule. The rule is also supported by the available data on base substitutions within the -1triplet.
停滞在缺陷型mRNA上的细菌核糖体可被兼具tRNA和mRNA功能的tmRNA拯救。tmRNA作为tRNA发挥功能时，在核糖体上进行的首个延伸循环非常特殊：tmRNA占据核糖体A位点时无需密码子与反密码子配对。我们的分析表明，在这种情况下，密码子与反密码子双链体的作用应由单个未配对的三联体完成。为了使tmRNA能够参与核糖体延伸循环，tmRNA的mRNA部分之前的三联体（-1三联体）应以A形式存在，且这种形式应被核糖体解码中心识别。由此得出一条规则，用于确定哪些三联体不能用作-1三联体。该规则用所有已知的414种tmRNA物种的-1三联体进行了测试。所有观察到的23种-1三联体均遵循制定的规则。关于-1三联体内碱基替换的现有数据也支持该规则。
