A restriction endonuclease map for the enzymes EcoRI, BamHI, SalI, and PstI covering 23.5 kilobase pairs (kb) of the srl recA region of Escherichia coli was constructed. An insertion of the transposon Tn10 in the negative regulatory gene srlR was shown to be located 5.8 kb away from the promoter proximal end of the recA gene. The extent of several Tn10 generated deletions, originating from the srlR301::Tn10 insertion, were analyzed by physical mapping. Three mutations that had removed the Tn10 encoded tetracycline resistance gene, del(srl-recA)302, del(srl-recA)304, and del(srl-recA)303, were found to be deleted for 40%, 45%, and 50% of the recA structural gene, respectively. A deletion, del(srl-recA)306, that had not affected the structure of the Tn10 in srlR301 was shown to have removed the entire recA structural gene.