Dual regulation of dnaK and groE operons by HrcA and Ca++ in Streptococcus pneumoniae

Abstract

The dnaK and groE operons in Streptococcus pneumoniae are repressed by HrcA in the presence of Ca(++). However, it is unclear how HrcA and Ca(++) regulate the dnaK and groE operons. This study examined the dual regulation of the dnaK and groE operons in S. pneumoniae by HrcA and Ca(++). At 30 degrees C, the hrcA mutant showed a constitutively higher level of dnaK expression at both the protein and mRNA levels than that of the wild type whereas the level of groEL expression was relatively unchanged. On the other hand, the levels of both dnaK and groEL transcripts were increased after heat shock but the hrcA mutant was not sensitive to heat shock. Immunoblot analysis of the cells pretreated with the Ca(++) chelator, BAPTA-AM, revealed the induction of HrcA and GroEL at both 30 degrees C and 42 degrees C. However, at longer preincubation time with BAPTA-AM, GroEL was further induced but the level of HrcA decreased suggesting that Ca(++) regulates the dnaK and groE operons differently. Overall, Ca(++) and HrcA differentially regulate the transcription of the dnaK and groE operons in S. pneumoniae. These results are expected to contribute to resolving the relationship between DnaK/GroEL expression and the pathogenesis in S. pneumoniae.