Characterization of HscC (Hsc62), homologue of Hsp70 in Escherichia coli: over-expression of HscC modulates the activity of house keeping sigma factor σ70.

Abstract Background: HscC, the third member of the Hsp70 family in Escherichia coli , shares 33% identity with the other two homologues, DnaK and HscA, and displays ATPase activity. Genetic and biochemical evidence indicates that the DnaK-DnaJ chaperone system interacts with σ32 and is involved in the negative regulation of the heat shock response. Although HscC is a highly conserved protein in the Hsp70 family, its function is still unknown. Results: We observed that the over-expression of HscC caused severe growth inhibition. To explore this effect, we performed primer extension analysis and a β-galactosidase assay and found that HscC reduced the σ70 -dependent promoter activity. An in vitro transcription assay revealed that HscC inhibited σ70 -dependent transcription. In addition, the co-purification analysis showed that σ70 co-eluted with HscC. Conclusion: These results indicate that HscC forms a complex with σ70 and may function as its negative modulator. [ABSTRACT FROM AUTHOR]