Mandecki W, Fowler A V, Zabin I
J Bacteriol. 1981 Aug;147(2):694-7. doi: 10.1128/jb.147.2.694-697.1981.
The position of the termination codon in lacZX90 was determined by isolation of a lac+ revertant. Lysine was found to replace tyrosine at position 1,012 of beta-galactosidase, indicating that X90 protein lacked the carboxyl-terminal 10 residues. A heat- and urea-sensitive hybrid enzyme was formed in vivo when supC, which supplies tyrosine to the position in the polypeptide corresponding to the nonsense codon, was used to suppress lacZX90. This result shows that suppression that adds back the original amino acid may not lead to the production of the wild-type enzyme if the latter is multimeric, because incomplete chains can be incorporated into the oligomer.
通过分离出一个乳糖操纵子阳性回复突变体，确定了lacZX90中终止密码子的位置。发现在β-半乳糖苷酶的第1012位赖氨酸取代了酪氨酸，这表明X90蛋白缺少羧基末端的10个残基。当使用supC（它为对应于无义密码子的多肽位置提供酪氨酸）来抑制lacZX90时，在体内形成了一种对热和尿素敏感的杂合酶。该结果表明，如果野生型酶是多聚体，那么添加回原始氨基酸的抑制可能不会导致野生型酶的产生，因为不完全的链可以掺入到寡聚体中。
