IDENTIFICATION AND CHARACTERIZATION OF HSIV HSIU (CLPQ CLPY) PROTEINSINVOLVED IN OVERALL PROTEOLYSIS OF MISFOLDED PROTEINS IN ESCHERICHIA-COLI

Heat shock response in Escherichia coli is autoregulated, Consistent w ith this, mutations in certain heat shock genes, such as dnaK, dnaJ, g rpE or htrC lead to a higher constitutive heat shock gene expression a t low temperatures, A similar situation occurs upon accumulation of ne wly synthesized peptides released prematurely from the ribosomes by pu romycin, We looked for gene(s) which, when present in multicopy, preve nt the constitutive heat shock response associated with htrC mutant ba cteria or caused by the presence of puromycin, One such locus was iden tified and shown to carry the recently sequenced hslV hslU (clpQ clpY) operon, HslV/ClpQ shares a very high degree of homology with members of the beta-type subunit, constituting the catalytic core of the 20S p roteasome. HslU/ClpY is 50% identical to the ClpX protein of E.coli, w hich is known to present large polypeptides to its partner, the ATP-in dependent proteolytic enzyme ClpP, We show that, in vivo, HslV and Hsl U interact and participate in the degradation of abnormal puromycylpol ypeptides. Biochemical evidence suggests that HslV/ClpQ is an efficien t peptidase whose activity is enhanced by HslU/ClpY in the presence of ATP.