Direct observation of single MuB polymers: evidence for a DNA-dependent conformational change for generating an active target complex.

MuB, an ATP-dependent DNA binding protein, is critical for selection of target sites on the host chromosome during Mu transposition. We have developed a system for observing the behavior of single MuB polymers bound to an immobilized molecule of DNA. We show that the individual polymers display a broad distribution of disassembly rates and exhibit regional variations in DNA binding. Additionally, ATP hydrolysis was obligatorily coupled to dissociation of MuB subunits from the DNA during polymer disassembly. We propose a model in which the formation of an active target complex is mediated by a conformational change within the MuB polymer that is influenced by the sequence of the DNA.