A NEW COMPONENT OF BACTERIOPHAGE-MU REPLICATIVE TRANSPOSITION MACHINERY - THE ESCHERICHIA-COLI CLPX PROTEIN

We have shown previously that some particular mutations in bacteriopha ge Mu repressor, the frameshift vir mutations, made the protein very s ensitive to the Escherichia coli ATP-dependent Clp protease. This enzy me is formed by the association between a protease subunit (ClpP) and an ATPase subunit. ClpA, the best characterized of these ATPases, is n ot required for the degradation of the mutant Mu repressors. Recently, a new potential ClpP associated ATPase, ClpX, has been described. We show here that this new subunit is required for Mu vir repressor degra dation. Moreover, ClpX (but not ClpP) was found to be required for nor mal Mu replication. Thus ClpX has activities that do not require its a ssociation with ClpP. In the pathway of Mu replicative transposition, the block resides beyond the strand transfer reaction, i.e. after the transposition reaction per se is completed, suggesting that ClpX is re quired for the transition to the formation of the active replication c omplex at one Mu end. This is a new clear-cut case of the Versatile ac tivity of polypeptides that form multicomponent ATP-dependent protease s.