Isolation of an ammonium or methylammonium ion transport mutant of Escherichia coli and complementation by the cloned gene.
Abstract
Isolation of an ammonium or methylammonium ion transport mutant of Escherichia coli and complementation by the cloned gene. A Jayakumar , S J Hwang , J M Fabiny , A C Chinault and E M Barnes Jr Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030. ABSTRACT During nitrogen-limited growth, Escherichia coli expresses a specific ammonium or methylammonium ion transport system (Amt). Strains carrying defects in Amt have been isolated following Tn10 transposon mutagenesis. These mutants have less than 10% of the transport activity of the parental strain. Glutamate, glutamine, arginine, or high levels (20 mM) of ammonium will serve as the sole nitrogen source for growth of these strains, and glutamine synthetase is normally expressed and repressed by the nitrogen regulatory (Ntr) system. When transformed with plasmid pGln84, containing lacZ fused to an Ntr promoter (glnLp), the Amt mutants expressed a normal level of beta-galactosidase. Furthermore, P1 bacteriophage transduction of the amt mutation into an Ntr mutant, normally constitutive for Amt, gave Amt- transductants. Therefore, the mutations are unlikely to lie within genes affecting Ntr elements. Following transformation with plasmid libraries of E. coli genomic DNA constructed in pUC9, two plasmids conferring the Amt+ phenotype on the amt mutants were isolated. These plasmids were unable to complement the Amt- phenotype of Ntr- mutants. Restriction digestion of these plasmids revealed common fragments, and Southern blot analyses indicated that the Amt-complementing sequence and the site of Tn10 insertion in the genome occur in the same 3.4-kilobase HindIII-SalI fragment. Insertion of TnphoA into this fragment produced amt::phoA fusions which gave high levels of alkaline phosphatase under nitrogen-limiting conditions but low levels during ammonia excess. This suggests that the amt product contains domains which are exported to the periplasm. CiteULike Connotea Delicious Digg Facebook Google+ Mendeley Reddit StumbleUpon Twitter What's this? « Previous | Next Article » Table of Contents This Article J. Bacteriol. February 1989 vol. 171 no. 2 996-1001 » Abstract PDF Classifications Research Article Services Email this article to a colleague Similar articles in ASM journals Alert me when this article is cited Alert me if a correction is posted Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of JB Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Load citing article information Citing articles via Web of Science Citing articles via Google Scholar Google Scholar Articles by Jayakumar, A. Articles by Barnes, E. M. Search for related content PubMed PubMed citation Articles by Jayakumar, A. Articles by Barnes, E. M. Related Content Load related web page information Social Bookmarking CiteULike Connotea Delicious Digg Facebook Google+ Mendeley Reddit StumbleUpon Twitter What's this? current issue December 2011, volume 193, issue 24 Alert me to new issues of JB About JB Subscribers Authors Reviewers Advertisers Inquiries from the Press Permissions & Commercial Reprints ASM Journals Public Access Policy JB RSS Feeds 1752 N Street N.W. • Washington DC 20036 202.737.3600 • 202.942.9355 fax • journals@asmusa.org Print ISSN: 0021-9193 Online ISSN: 1098-5530 Copyright © 2011 by the American Society for Microbiology. For an alternate route to JB .asm.org, visit: http://intl- JB .asm.org | More Info» var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www."); document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E")); var pageTracker = _gat._getTracker("UA-5821458-9"); pageTracker._trackPageview();