GENETIC MAPPING OF CHL C GENE OF NITRATE REDUCTASE A SYSTEM IN ESCHERICHIA COLI K12

Nitrate reductase A is a component of an electron transport system, using NO3- as the final acceptor. Inside the cell, the enzyme is associated with the cellular membrane, and it is found in the particulate fractions of cell-free extracts (1, 2). Chlorate reduction which is effected by nitrate reductase A (3), is a reaction lethal to the cell. Therefore, mutants that have defective nitrate reductase are resistant to ClO3- (chl-) (4). The high frequency of the mutation chl+ → chl- (10-5), reflets the polygenic control of the electron transport system associated with nitrate reductase. All chl mutants lack nitrate reductase activity. Formic-hydrogenlyase activity is lost simultaneously in 99 % of them. The 1 % of chl mutants that retain formic hydrogenlyase activity are those altered in the chl C gene (5). By mutation of 4 different genes (chl A, chl B, chl D and chl E) the pleiotropic phenotype is obtained. Preliminary experiments (6) indicate that the chl C gene is linked to the trp region. The present paper reports a more accurate mapping. © 1969.