期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1980
卷号：77
期号：6
页码：3249-3253
DOI：10.1073/pnas.77.6.3249
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：In order to isolate functional Escherichia coli aspartate carbamoyltransferase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC2.1.3.2) with single amino acid replacements, a series of pyrB nonsense mutants has been isolated. These nonsense mutants were induced by 2-aminopurine mutagenesis and selected by a combination of antibiotic treatments, direct enzyme assays, and suppressibility tests. Suppression of the pyrB nonsense mutation with various suppressors, which insert different amino acids, has resulted in the formation of a series of mutant aspartate carbamoyltransferases, each differing in one amino acid from the wild-type enzyme. After partial purification, kinetic studies revealed that some of the mutant enzymes had altered homotropic and heterotropic interactions. The mutants that had a tyrosine insert showed the most pronounced changes, followed by those with a serine insert. The mutants having a glutamine insert, howevr, were indistinguishable from the wild-type enzyme, supporting the conclusion that, because of the specificity of the mutagen, the glutamine insert had regenerated the wild-type enzyme.
