Organization and expression of the dnaJ and dnaK genes of Escherichia coli K12.

A temperature-sensitive mutation in the dnaJ gene of Escherichia coli K12 is described which affects replication of the bacterial DNA. The gene is located adjacent to the dnaK gene described previously (Saito and Uchida, 1977). The physical and functional organization of the dnaJ-dnaK region was studied in detail by analyzing the heteroduplexes and functions of various deletion mutants of lambdadnaJdnaK, a transducing phage carrying both of the dna genes. The sizes of dnaJ and dnaK cistrons were estimated to be at most 1.2 +/- 0.5 and 2.1 +/- 0.4 kilobases, respectively. In vivo expression of the dnaJ function by various deletion phages indicated that the dnaK and dnaJ cistrons were transcribed from a promoter located at the head of the dnaK cistron, dnaJ being downstream to dnaK. Presence of a weak promoter which reads only the dnaJ cistron was also suggested. A simple method for isolating independent deletion mutants of phage lambda was described.