DISASSEMBLY OF THE MU-TRANSPOSASE TETRAMER BY THE CLPX CHAPERONE

Mu transposition is promoted by an extremely stable complex containing a tetramer of the transposase (MuA) bound to the recombining DNA. Her e we purify the Escherichia coli ClpX protein, a member of a family of multimeric ATPases present in prokaryotes and eukaryotes (the Clp fam ily), on the basis of its ability to remove the transposase from the D NA after recombination. Previously, ClpX has been shown to function wi th the ClpP peptidase in protein turnover. However, neither ClpP nor a ny other protease is required for disassembly of the transposase. The released MuA is not modified extensively, degraded, or irreversibly de natured, and is able to perform another round of recombination in vitr o. We conclude that ClpX catalyzes the ATP-dependent release of MuA by promoting a transient conformational change in the protein and, there fore, can be considered a molecular chaperone. ClpX is important at th e transition between the recombination and DNA replication steps of tr ansposition in vitro; this function probably corresponds to the essent ial contribution of ClpX for Mu growth. Deletion analysis reveals that the sequence at the carboxyl terminus of MuA is important for disasse mbly by ClpX and can target MuA for degradation by ClpXP in vitro. The se data contribute to the emerging picture that members of the Clp fam ily are chaperones specifically suited for disaggregating proteins and are able to function with or without a collaborating protease.