VERSATILE ACTION OF ESCHERICHIA-COLI CLPXP AS PROTEASE OR MOLECULAR CHAPERONE FOR BACTERIOPHAGE-MU TRANSPOSITION

The molecular chaperone ClpX of Escherichia coli plays two distinct fu nctions for bacteriophage Mu DNA replication by transposition, As spec ificity component of a chaperone-linked protease, it recognizes the Mu immunity repressor for degradation by the peptidase component ClpP, t hus derepressing Mu transposition functions, After strand exchange has been promoted by MuA transposase, ClpX alone can alter the conformati on of the transpososome (the complex of MuA with Mu ends), and the rem odeled MuA promotes transition to replisome assembly, Although ClpXP c an degrade MuA, the presence of both ClpP and ClpX in the reconstitute d transposition system did not destroy MuA essential for initiation of DNA replication by specific host replication enzymes, Levels of ClpXP needed to overcome inhibition by the repressor did not prevent MuA fr om promoting strand transfer, and ClpP stimulated alteration of the tr anspososome by ClpX Apparently intact MuA was still present in the res ulting transpososome, promoting initiation of Mu DNA replication by sp ecific replication enzymes, The results indicate that ClpXP can discri minate repressor and MuA in the transpososome as substrates of the pro tease or the molecular chaperone alone, degrading repressor while remo deling MuA for its next critical function.