CLPX PROTEIN OF ESCHERICHIA-COLI ACTIVATES BACTERIOPHAGE-MU TRANSPOSASE IN THE STRAND TRANSFER COMPLEX FOR INITIATION OF MU-DNA-SYNTHESIS

During transposition bacteriophage Mu transposase (MuA) catalyzes the transfer of a DNA strand at each Mu end to target DNA and then remains tightly bound to the Mu ends. Initiation of Mu DNA replication on the resulting strand transfer complex (STC1) requires specific host repli cation proteins and host factors from two partially purified enzyme fr actions designated Mu replication factors alpha and beta (MRF alpha an d beta). Escherichia coli ClpX protein, a molecular chaperone, is a co mponent required for MRF alpha activity, which removes MuA from DNA fo r the establishment of a Mu replication fork. ClpX protein alters the conformation of DNA-bound MuA and converts STC1 to a less stable form (STC2). One or more additional components of MRF alpha (MRF alpha(2)) displace MuA from STC2 to form a nucleoprotein complex (STC3), that re quires the specific replication proteins and MRF beta for Mu DNA synth esis. MuA present in STC2 is essential for its conversion to STC3. If MuA is removed from STC2, Mu DNA synthesis no longer requires MRF alph a(2), MRF beta and the specific replication proteins. These results in dicate that ClpX protein activates MuA in STC1 so that it can recruit crucial host factors needed to initiate Mn DNA synthesis by specific r eplication enzymes.