HscA is involved in the dynamics of FtsZ-ring formation in Escherichia coli K12

Background: FtsZ, a homologue of eukaryotic tubulin, localizes throughout t he cytoplasm in non-dividing Escherichia coli. However, it assembles in cyt okinetic rings at the early stages of septation. Factors controlling the dy namics of FtsZ ring formation are unknown, and the molecular mechanism gove rning these dynamics is yet to be determined. Results: At 42 degreesC, JE10715 mutant bacteria formed multinucleated fila ments with a highly reduced number of FtsZ-rings at potential division site s. The JE10715 phenotype resulted from a mis-sense mutation in the hscA gen e 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 c onditions exhibited longer rod cells with an abnormal localization of FtsZ. The over-expression of dnaK partially complemented the JE10715 mutation. I n vitro, the ATPase activity of the mutant protein HscA715 was reduced to 6 3% 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-lik e interaction with FtsZ. Defects in hscA, however, can partially be compens ated for by redundant genes, including the wild-type dnaK.