The ClpP component of Clp protease is the sigma 32-dependent heat shock protein F21.5.

The genes that encode the subunits of the Clp protease of Escherichia coli, clpA and clpP, appear to be regulated differently from each other. The clpA gene does not seem to be under heat shock control (Y. S. Katayama, S. Gottesman, J. Pumphrey, S. Rudikoff, W. P. Clark, and M. R. Maurizi, J. Biol. Chem. 263:15226-15236, 1988). In contrast, the level of ClpP protein was increased in rpoH+ cells but not in null rpoH cells after an upshift in temperature from 17 to 43 degrees C. The level of ClpP protein in a null dnaK strain was also elevated relative to the level of ClpP protein in an otherwise isogenic dnaK+ strain. In two-dimensional gels, the ClpP protein was located in the position of the previously unidentified heat shock protein F21.5. No protein spot corresponding to F21.5 was present in two-dimensional gels of a null clpP strain. The clpP gene, therefore, appears to be a heat shock gene, expressed in a sigma 32-dependent manner and negatively regulated by DnaK; the product of clpP is the previously unidentified heat shock protein F21.5.