A STUDY OF THE DOUBLE MUTATION OF DNAJ AND CBPA, WHOSE GENE-PRODUCTS FUNCTION AS MOLECULAR CHAPERONES IN ESCHERICHIA-COLI

The CbpA protein is an analog of the DnaJ molecular chaperone of Esche richia call. To gain insight into the function of CbpA, we examined th e nature of a cbpA null mutation with special reference to those of dn aK and dnaJ null mutations. In particular, the cbpA dnaJ double-null m utant was found to exhibit severe defects in cell growth, namely, a ve ry narrow temperature range for growth, a defect in cell division, and susceptibility to killing by carbon starvation. These phenotypes are very similar to those reported for dnaK null mutants but not to those of dnaJ null mutants. Our results are best interpreted by assuming tha t CbpA is capable of compensating for DnaJ for cell growth and thus Ch at the function(s) of CbpA is closely related to that of DnaJ.