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：1981
卷号：78
期号：4
页码：2135-2139
DOI：10.1073/pnas.78.4.2135
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The nitrogen regulatory locus "glnR" of Escherichia coli and Salmonella typhimurium is composed of two cistrons, which we propose to call ntrB and ntrC (nitrogen regulation B and C). Frameshift mutations in ntrB and ntrC were isolated on a lambda phage that carries the E. coli ntrB and ntrC genes and the closely linked glnA gene, the structural gene encoding glutamine synthetase [L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2 ]; mutations were selected as suppressors of glnF (which we propose to rename ntrA), a selection used previously to isolate glnR mutations. Phage DNA from one mutant (ntrB) failed to direct synthesis of a 36-kilodalton (kDal) protein whose synthesis was directed by DNA from the parent phage (ntrB+) in a coupled in vitro transcription/translation system. DNA from three other mutants (ntrC) failed to direct synthesis of a 54-kDal protein; DNA from two of these mutants instead directed synthesis of smaller proteins, 53 and 50 kDal, respectively. In all four cases, DNA from frameshift revertants directed synthesis of both the 36-kDal and 54-kDal proteins. These results suggested that ntrB and ntrC were separate genes which encoded 36-kDal and 54-kDal protein products, respectively. Frameshift mutations in ntrB and ntrC complemented each other with regard to regulation of glnA expression in vivo and growth on arginine as nitrogen source, another nitrogen-controlled phenotype; this confirmed that ntrB and ntrC are separate cistrons that encode diffusible products. The ntrB and ntrC genes were also defined in S. typhimurium. Studies of mutant strains provided information on the roles of the ntrB and ntrC products in activation and repression of glnA expression and raised the possibility that these products function as a protein complex in regulating expression of nitrogen-controlled genes.
