Mottagui-Tabar S, Björnsson A, Isaksson L A
Department of Microbiology, Stockholm University, Sweden.
EMBO J. 1994 Jan 1;13(1):249-57. doi: 10.1002/j.1460-2075.1994.tb06255.x.
Forty-two different sense codons, coding for all 20 amino acids, were placed at the ribosomal E site location, two codons upstream of a UGA or UAG codon. The influence of these variable codons on readthrough of the stop codons was measured in Escherichia coli. A 30-fold difference in readthrough of the UGA codon was observed. Readthrough is not related to any property of the upstream codon, its cognate tRNA or the nature of its codon-anticodon interaction. Instead, it is the amino acid corresponding to the second upstream codon, in particular the acidic/basic property of this amino acid, which seems to be a major determinant. This amino acid effect is influenced by the identity of the A site stop codon and the efficiency of its decoding tRNA, which suggests a correlation with ribosomal pausing. The magnitude of the amino acid effect is in some cases different when UGA is decoded by a wildtype form of tRNA(Trp) as compared with a suppressor form of the same tRNA. This indicates that the structure of the A site decoding tRNA is also a determinant for the amino acid effect.
42种不同的有义密码子，编码所有20种氨基酸，被置于核糖体E位点位置，即位于UGA或UAG密码子上游两个密码子处。在大肠杆菌中测定了这些可变密码子对终止密码子通读的影响。观察到UGA密码子通读有30倍的差异。通读与上游密码子的任何特性、其同源tRNA或其密码子-反密码子相互作用的性质均无关。相反，似乎主要决定因素是对应于第二个上游密码子的氨基酸，特别是该氨基酸的酸性/碱性性质。这种氨基酸效应受A位点终止密码子的身份及其解码tRNA的效率影响，这表明与核糖体停顿有关。与相同tRNA的抑制形式相比，当UGA由野生型tRNA(Trp)解码时，氨基酸效应的大小在某些情况下有所不同。这表明A位点解码tRNA的结构也是氨基酸效应的一个决定因素。
