IDENTIFICATION AND CHARACTERIZATION OF A NEW ESCHERICHIA-COLI GENE THAT IS A DOSAGE-DEPENDENT SUPPRESSOR OF A DNAK DELETION MUTATION

We report the isolation and characterization of a previously unidentified Escherichia coli gene that suppresses the temperature-sensitive growth and filamentation of a dnaK deletion mutant strain. Introduction of a multicopy plasmid carrying this wild-type gene into a dnaK deletion mutant strain rescued the temperature-sensitive growth of the dnaK deletion mutant strain at 40.5°C and the filamentation, fully at 37°C and partially at 40.5°C. However, the inability of dnaK mutant cells to support bacteriophage λ growth was not suppressed. This gene was also able to suppress the temperture-sensitive growth of a grpE280 mutant strain at 41°C. Filamentation of the grpE280 mutant strain was suppressed at 37°C but not at 41°C. The dnaK suppressor gene, designated dksA, maps near the mrcB gene (3.7 min on the E. coli chromosome). DNA sequence analysis and in vivo experiments showed that dksA encodes a 17,500-M(r) polypeptide. Gene disruption experiments indicated that dksA is not an essential gene.