Characterization of HscC (Hsc62), homologue of Hsp70 in Escherichia coli: over-expression of HscC modulates the activity of house keeping sigma factor sigma70.
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 sigma32 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 beta-galactosidase assay and found that HscC reduced the sigma70-dependent promoter activity. An in vitro transcription assay revealed that HscC inhibited sigma70-dependent transcription. In addition, the co-purification analysis showed that sigma70 co-eluted with HscC.


CONCLUSIONS
These results indicate that HscC forms a complex with sigma70 and may function as its negative modulator.
Arifuzzaman
Mohammad
M
Department of Cell Biology, NARA Institute of Science and Technology, Ikoma 630-0101, Japan.
Oshima
Taku
T
Nakade
Shinsuke
S
Mori
Hirotada
H
D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012808:Sigma Factor / Q000378:metabolism*
D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D012808:Sigma Factor; C114584:hscC protein, E coli; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; C063842:dnaK protein, E coli