Characterization of the dnaA gene carried by lambda transducing phage

Summary

Specialized transducing phages λdnaA were obtained by inducing lysogens in which λtna was integrated at the tnaA region of the Escherichia coli chromosome; the tnA region is located in the vicinity of the dnaA gene. The dnaA ^- deletion derivatives of λdnaA were isolated from the lysate of λdnaA grown on bacteria carrying a transposon Tn3.

The structures of various transducing phages thus obtained were determined by heteroduplex DNA mapping. From these results, the transducing fragment of 13.8-kb-long was divided into nine domains. Upon infection of UV-irradiated cells with the phage, production of polypeptides of 49 kD and 42 kD was specifically associated with infections by the dnaA and recF transducing phages. Polypeptides of 49 kD and 42 kD appeared to be coded for by dnaA and recF genes, respectively. The dnaA gene was assigned to the region of 2.8-kb-long which extends by 2.4 kb in the counterclockwise direction on the E. coli genetic map and 0.4 kb in the opposite direction, as measured from the nearest HindIII site close to the tnaA gene. The recF gene was also discovered to lie very close to dnaA in the order of tnaA-dnaA-recF.

Merogenotes heterozygous for the dnaA gene were constructed by introducing F′100-12 carrying λdnaA into the recipients with different mutations at or near dnaA. For combinations, F′(λdnaA ⁺)/dnaA46 and F′(λdna ⁺)/dna-83, dnaA ⁺ was trans-dominant, whereas the dnaA ⁺ was recessive for F′(λdnaA ⁺)/dna-5. For F′(λdnaA ⁺)/dna-167, the result of the transdominance test was affected by the growth media employed; dnaA ⁺ was dominant on a λ-broth plate, and dna-167 was dominant on an M9-minimal plate. Thus, transdominance of dnaA ⁺ in heterozygotes is affected by difference in mutations and growth media.