THE 65-KDA PROTEIN-DERIVED FROM THE INTERNAL TRANSLATIONAL START SITEOF THE CLPA GENE BLOCKS AUTODEGRADATION OF CLPA BY THE ATP-DEPENDENT PROTEASE TI IN ESCHERICHIA-COLI

The ATP-dependent protease Ti consists of two different components: Cl pA containing ATP-cleaving sites and ClpP hating serine active sites f or proteolysis, The clpA gene has dual translational start sites and t herefore encodes two polypeptides with sizes of 84 and 65 kDa (referre d to as ClpA84 and ClpA65, respectively), Here me show that ClpA84, bu t not ClpA65, is degraded in vitro by ClpP in the presence of ATP, The ClpP-mediated hydrolysis of ClpA84 could be prevented by casein, whic h is an excellent substrate of protease Ti (i,e, ClpA84/ClpP complex), Thus, it appears that free form of ClpA84 competes with casein for th e degradation by ClpA/ClpP complex, Furthermore, ClpA65 inhibited the auto-degradation of ClpA84 by the complex, These results suggest that ClpA65 may play an important role in the control of the ClpA84 level a nd in turn in the regulation of ATP-dependent protein breakdown in E, coli.