Interestingly, in bacteria, HSP chaperones are often directly involved in regulation of Naltrindole hydrochloride transcription through interactions with transcription MRS 1220 regulators or sigma factors. This contribution can be either positive, or negative. Molecular chaperones of the Hsp70 class bind and stabilize proteins at intermediate stages of folding, degradation, assembly and translocation across membranes. They are required for growth at normal temperatures, but their level of expression is enhanced under conditions of stress. The most important for bacterial viability and the most extensively characterized Hsp70 chaperone in Escherichia coli is DnaK. The activity of DnaK/ Hsp70 chaperones is regulated by co-chaperones, members of the DnaJ/Hsp40 family. DnaJ is composed of four domains. The N-terminal strongly conserved,70 residue long so called Jdomain, the central cysteine-rich domain and two C-terminal domains of similar fold. DnaJ stimulates ATPase activity of DnaK, through conformational change in DnaK from the ATP-bound state, which binds substrates weakly, to an ADP-bound state, which binds substrates tightly. Biochemical studies on the E. coli DnaK�CDnaJ system have shown that the J-domain, and in particular its H-P-D sequence motif, is important for both DnaK binding and ATPase stimulation. These processes are mediated by direct interaction between the J-domain of a cochaperone and the ATPase domain of DnaK/Hsp70. Jdomains and their mechanism of chaperone regulation are highly conserved from bacteria to humans. Among the three Hsp40 proteins that function as DnaK cochaperone, only CbpA is regulated through interaction with a specific partner protein, CbpM. The biological processes regulated by CbpM are only beginning to be understood. Its gene lies downstream of cbpA within the same operon and is homologous to proteins encoded by genes located downstream of dnaJ-like genes in a diverse range of bacteria. It has been shown that CbpM inhibits both CbpA co-chaperone activity and its DNA binding. It has been suggested that during certain growth phase or stress conditions, CbpA might be released from CbpM and recruit DnaK to function as a co-chaperone. Unexpectedly, we observed that CbpM displays striking structural similarity to MerR-like transcription regulators and at the same time an architectural difference, which reflects different function of these two groups of proteins. The structural similarity suggests the evolution of function of an ancient protein family from transcription regulation to chaperone system regulation and we propose a mechanistic model explaining such a transition. Sequence analysis clearly supports a relationship between CbpM and MerR-like transcriptional regulators, as numerous related sequences can be identified using PSI-BLAST with the E. coli CbpM sequence as bait, with scores of,1024.