Identification of a new locus in the Escherichia coli cotransduction gap that represents a new genetic component of the L-asparagine utilization system.

A temperature-sensitive Escherichia coli mutant defective for the ability to utilize L-asparagine as a sole nitrogen source was isolated after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. The mutation (asu) produces two distinct phenotypic effects. Mutant strains grow poorly at high temperature on minimal plates containing asparagine as the sole nitrogen source; this effect is greatly exacerbated by the presence of methionine. Mutant strains utilize L-asparagine as a nitrogen source three to four times more efficiently at permissive temperatures than the wild-type strains. The mutation maps at 32.4 min on the E. coli chromosome, within the E. coli cotransduction gap. Mutant strains produce normal amounts of thermo-stable L-asparaginase I activity. The mutation therefore affects a component of the asparagine utilization system other than the catabolism of asparagine within the cell; it probably affects asparagine uptake.