An essential gene (efg) located at 38.1 minutes on the Escherichia coli chromosome.

An Escherichia coli gene which is able to complement "ammonia-dependent growth" (adgA) mutations in Rhodobacter capsulatus was previously isolated from an R-prime plasmid and was shown to be located between 34 and 39 min on the E. coli chromosome (3). In the present study, a 10.9-kb HindIII-PstI fragment of genomic DNA was cloned from E. coli HB101 and shown to complement adgA mutations in R. capsulatus. Restriction mapping of this fragment and comparison with the restriction map of the E. coli chromosome (5) (Fig. 1) showed that the complementing gene is located at 38.1 min (1840 kbp) on the E. coli genetic map. The restriction map of this fragment was identical to that of Kohara et al. (5), except for the presence of an additional EcoRV site. The chromosomal location of the gene is identical to that proposed by Kim and Wulff (4) on the basis of the partial sequence of an 8.0-kb DNA fragment. Restriction fragments containing the Kmr gene from pUC4-KIXX (Pharmacia-LKB) were inserted, in both orien-