BACKGROUND: FtsZ, a homologue of eukaryotic tubulin, localizes throughout the cytoplasm in non-dividing Escherichia coli. However, it assembles in cytokinetic rings at the early stages of septation. Factors controlling the dynamics of FtsZ ring formation are unknown, and the molecular mechanism governing these dynamics is yet to be determined. RESULTS: At 42 degrees C, JE10715 mutant bacteria formed multinucleated filaments with a highly reduced number of FtsZ-rings at potential division sites. The JE10715 phenotype resulted from a mis-sense mutation in the hscA gene which encodes a heat shock Hsp70 family protein, with a single alanine-to-valine substitution at position 192 within the ATPase domain. Both JE10715 and the hscA knockout strain of JE10715 were completely complemented by a plasmid-born, wild-type hscA gene, but not by a mutant-type hscA715 gene. An hscA conditional knockout of the wild-type strain under non-permissive conditions exhibited longer rod cells with an abnormal localization of FtsZ. The over-expression of dnaK partially complemented the JE10715 mutation. In vitro, the ATPase activity of the mutant protein HscA715 was reduced to 63% of wild-type HscA activity. HscA co-sedimented with FtsZ-polymers in the presence of GTP. CONCLUSION: HscA is involved in FtsZ-ring formation, through a chaperon-like interaction with FtsZ. Defects in hscA, however, can partially be compensated for by redundant genes, including the wild-type dnaK.

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