Here, we report the cloning of a 5.8-kb PstI fragment of chromosomal DNA from Bacillus stearothermophilus (Bt) carrying the three genes, grpE, dnaK and dnaJ. This fragment contains, in addition, the 3'-end of an open reading frame which has been shown to be part of the dnaK operon in three bacterial species. The dnaJ gene could complement an Escherichia coli dnaJts mutant for growth at high temperature. Sequencing and hybridization data strongly suggest that the Bt chromosome contains an analog of dnaJ.