CLPX AND MUB INTERACT WITH OVERLAPPING REGIONS OF MU-TRANSPOSASE - IMPLICATIONS FOR CONTROL OF THE TRANSPOSITION PATHWAY

Transposition of phage Mu is catalyzed by an extremely stable transpos ase-DNA complex. Once recombination is complete, the Escherichia coli ClpX protein, a member of the Clp/Hsp100 chaperone family, initiates d isassembly of the complex for phage DNA replication to commence. To un derstand how the transition between recombination and replication is c ontrolled, we investigated how transposase-DNA complexes are recognize d by ClpX. We find that a 10-amino-acid peptide from the carboxy-termi nal domain of transposase is required for its recognition by ClpX. Thi s short, positively charged peptide is also sufficient to convert a he terologous protein into a ClpX substrate. The region of transposase th at interacts with the transposition activator, MuB protein, is also de fined further and found to overlap with that recognized by ClpX. As a consequence, MuB inhibits disassembly of several transposase-DNA compl exes that are intermediates in recombination. This ability of MuB to b lock access to transposase suggests a mechanism for restricting ClpX-m ediated remodeling to the proper stage during replicative transpositio n. We propose that overlap of sequences involved in subunit interactio ns and those that target a protein for remodeling or destruction may b e a useful design for proteins that function in pathways where remodel ing or degradation must be regulated.