MukE and MukF form two distinct high affinity complexes.

The MukBFE complex is essential for chromosome segregation and condensation in Escherichia coli. MukB is functionally related to the structural maintenance of chromosomes (SMC) proteins. Similar to SMCs, MukB requires accessory proteins (MukE and MukF) to form a functional complex for DNA segregation. MukF is a member of the kleisin family, which includes proteins that commonly mediate the interaction between SMCs and other accessory proteins, suggesting that the similarities between the MukBFE and the SMC complexes extend beyond MukB. Although SMCs have been carefully studied, little is known about the roles of their accessory components. In the present work, we characterize the oligomeric states of MukE and MukF using size exclusion chromatography and analytical ultracentrifugation. MukE self-associates to form dimers (K(D) 18 +/- 3 mum), which in turn interact with the MukF dimer to form two distinct high affinity complexes having 2:2 and 2:4 stoichiometries (F:E). Intermediate complexes are not found, and thus we propose that the equilibrium between these two complexes determines the formation of a functional MukBFE with stoichiometry 2:2:2.