Genetic and biomedical studies demonstrating a second gene coding for asparagine synthetase in Escherichia coli

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Abstract
Genetic experiments indicated that asparagine auxotrophs of E. coli K-12 can be made asparagine prototrophs at either of 2 sites on the chromosome and that wild-type strains require both sites to be mutated to produce asparagine auxotrophy. The former asn locus is now called asnA, and the new gene is designated asnB. The asnB gene is located near gal. AsnA+ asnB and asnA asnB+ strains were constructed, and the asparagine synthetic reaction was characterized in extracts. The asnA gene codes for the enzyme previously described, whereas the asnB gene is involved in the production of an enzyme which differs from the one previously described in its specific activity in extracts, its stability at low and high temperatures and its apparent ability to use either glutamine or NH3 as amide nitrogen donor. Physiological studies showed that either enzyme alone is sufficient to allow a maximal growth rate under conditions of asparagine limitation.