Abstract
DNA was prepared from a strain of E. coli bearing a mutation which confers the GlnC phenotype (inability to reduce the expression of glnA and other N-regulated operons in response to ammonia in the growth medium). A fragment of this DNA carrying glnA, the structural gene for glutamine synthetase, was cloned on plasmid pBR322. By using recombination in vitro, one mapped the GlnC mutation to a region between glnA and glnG. This region defines a gene, glnL, which codes for a trans-acting product; the GlnC mutant produces an altered product. The glnL product plays a key role in the communication of information concerning the quality and abundance of the N source in the growth medium to a destination responsible for the regulation of glnA and other genes for enzymes responsible for N utilization.