DnaK is a major antigen in Streptococcus pneumoniae, and is induced by a minor shift in temperature (30 to 37¡ÆC) but not by ethanol shock. Although HrcA in the presence of Ca++ represses the expression of both groEL and hrcA, the control of transcription of the dnaK operon is not completely understood. In this study, the dnaK operon of S. pneumoniae (5? hrcA-grpE-dnaK-dnaJ) was cloned and analyzed. It contains large intergenic regions in grpE/dnaK and dnaK/dnaJ. Pulse labeling with [35S]-methionine and immunoblot analyses revealed the presence of higher levels of DnaK than of HrcA even in the presence of Ca++ after heat shock suggesting that Ca++ differentially regulates the heat shock responses of hrcA and dnaK. By blocking de novo mRNA synthesis with rifampin it was shown that neither the hrcA nor the groEL transcripts were stabilized by heat shock even though dnaK transcripts were stabilized. We conclude that S. pneumoniae uses fine regulation of the transcription of the individual genes of the tetracistronic dnaK operon to cope with the various stresses experienced during infections.

Keywords: Calcium, HrcA, dnaK Operon, Streptococcus pneumoniae