Complex formation of MukB, MukE and MukF proteins involved in chromosome partitioning in Escherichia coli

mukF, mukE and mukB genes are essential for the process of chromosome parti tioning in Escherichia coil, We have studied protein-protein interactions a mong MukB, MukE and MukF proteins by co-immunoprecipitation and sucrose gra dient 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 an d MukE bind the C-terminal globular domain of MukB, MukF is indispensable f or an interaction between MukB and MukE; however, MukF itself is able to as sociate 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 com plex either with MukE or MukB, a complex consisting of the three Muk protei ns was barely detected in vitro. However, increasing the Ca2+ or Mg2+ conce ntration in the reaction partially restored complex formation. This suggest s that Ca2+ or Mg2+ may be required for the formation of a complex consisti ng of the three Muk proteins, and thus may participate in a particular step during chromosome partitioning.