PHYSICAL AND BIOCHEMICAL-ANALYSIS OF THE CLONED RECB-GENE AND RECC-GENE OF ESCHERICHIA-COLI K-12

A 19-kilobase BamHI fragment encoding the recB (exonuclease V), recC (exonuclease V), ptr (protease III), thyA and argA genes of E. coli K-12 was cloned into a multicopy plasmid (pCDK3). In E. coli maxicells, the plasmid specified the synthesis of 7 polypeptides of 140,000 (recC), 128,000 (recB), 110,000 (ptr), 53,000 (argA), 50,000, 33,000 (thyA) and 22,000 MW as well as .beta.-lactamase and chloramphenicol acetyltransferase. From analysis of subclones and Tn1000 insertions, it appears that the 110,000 and 50,000 MW proteins originated from the ptr DNA coding sequence which is located between the recB and recC genes. Although recC, ptr and recB were physically closely linked and transcribed in the same direction, they do not appear to constitute an operon. Cells carrying pCDK3 contained a 30- to 50-fold increase in exonuclease V activity, without affecting cell viability.