The nucleotide sequence downstream from the Bordetella resistance to killing (brk) locus in Bordetella pertussis was determined. Analysis of the sequence revealed an operon consisting of two highly predicted open reading frames (ORFs). The deduced amino-acid sequence of each ORF has strong homologies to the heat-shock proteins/chaperonins Cpn60 and Cpn10. The promoter contains consensus sequences for both sigma 32 and sigma 70 binding, and it possesses the CIRCE regulatory inverted repeat. A potential Rho-independent terminator was identified and appears to be shared with the brkA gene.