In E.coli the heat shock response, which alters the proteins produced by the cell at different temperatures, is mediated by

A)degradation of chaperone proteins at high temperatures.
B)denaturing of DNA in the promoters in the genes of heat-sensitive proteins.
C)synthesis of alternative sigma factors at high temperatures to activate transcription of heat-shock genes.
D)increasing the promoter affinity of already existing polymerase sigma factors at high temperatures.