SummaryThe assembly of ring-like structures, composed of FtsZ proteins (i.e. the Z ring), is the earliest and most essential process in bacterial cytokinesis. It has been shown that this process is directly regulated by the FtsZ-binding proteins, FtsA, ZapA, and EzrA, in Bacillus subtilis . In this study, protein complexes that are involved in Z-ring formation were chemically crosslinked in vivo , purified by affinity chromatography, and analysed by mass spectrometry.