Alam S L, Wills N M, Ingram J A, Atkins J F, Gesteland R F
University of Utah, 15 N. 2030 E. Room 6160, Salt Lake City, UT, 84112-5330, USA.
J Mol Biol. 1999 May 21;288(5):837-52. doi: 10.1006/jmbi.1999.2713.
Retroviruses, such as murine leukemia virus (MuLV), whose gag and pol genes are in the same reading frame but separated by a UAG stop codon, require that 5-10 % of ribosomes decode the UAG as an amino acid and continue translation to synthesize the Gag-Pol fusion polyprotein. A specific pseudoknot located eight nucleotides 3' of the UAG is required for this redefinition of the UAG stop codon. The structural probing and mutagenic analyses presented here provide evidence that loop I of the pseudoknot is one nucleotide, stem II has seven base-pairs, and the nucleotides 3' of stem II are important for function. Stem II is more resistant to single-strand-specific probes than stem I. Sequences upstream of the UAG codon allow formation of two competing structures, a stem-loop and the pseudoknot.
逆转录病毒，如鼠白血病病毒（MuLV），其gag和pol基因位于同一阅读框中，但被一个UAG终止密码子隔开，这就要求5%至10%的核糖体将UAG解码为一种氨基酸，并继续翻译以合成Gag-Pol融合多蛋白。UAG终止密码子的这种重新定义需要一个位于UAG下游8个核苷酸处的特定假结。本文进行的结构探测和诱变分析提供了证据，表明假结的环I为一个核苷酸，茎II有七个碱基对，茎II下游的核苷酸对功能很重要。茎II比茎I对单链特异性探针更具抗性。UAG密码子上游的序列允许形成两种相互竞争的结构，一种茎环结构和假结结构。
