• Ca2+-binding protein;
  • chromosome partitioning;
  • motor protein;
  • MukB–MukE–MukF

mukF, mukE and mukB genes are essential for the process of chromosome partitioning in Escherichia coli. We have studied protein–protein interactions among MukB, MukE and MukF proteins by co-immunoprecipitation and sucrose gradient sedimentation experiments, using mukFEB null cells harboring plasmids carrying the wild-type or mutant-type mukFEB operon. MukB forms a complex with MukF and MukE. Analysis of mutant MukB proteins suggested that MukF and MukE bind the C-terminal globular domain of MukB. MukF is indispensable for an interaction between MukB and MukE; however, MukF itself is able to associate with MukB even in the absence of MukE. We have also found that MukF has a Ca2+-binding activity. Although purified MukF was able to make a complex either with MukE or MukB, a complex consisting of the three Muk proteins was barely detected in vitro. However, increasing the Ca2+ or Mg2+ concentration in the reaction partially restored complex formation. This suggests that Ca2+ or Mg2+ may be required for the formation of a complex consisting of the three Muk proteins, and thus may participate in a particular step during chromosome partitioning.