Identification of a New Locus in the Escherichia coli Cotransduction Gap that Represents a New Genetic Component of the L-Asparagine Utilization System

Department of Zoology and Physiology, Rutgers University, Newark, NJ 07102, USA ABSTRACT Summary: 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. (1) 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. (2) 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.