Stringent response in Escherichia coli induces expression of heat shock proteins

The rpoD gene (encoding the 70,000 Mr sigma subunit of Escherichia coli RNA polymerase) is the most distal gene in an operon that contains three genes. The promoter-proximal gene is rpsU (encoding ribosomal protein S21) and the middle gene is dnaG (encoding DNA primase). During the stringent response, caused by a deficiency in an aminoacyl-tRNA, expression of rpsU is decreased, while expression of rpoD is not. This disco-ordinate regulation is due to increased transcription from a minor promoter upstream from rpoD, in the dnaG gene. Transcription from this promoter is also increased during the heat shock response. Expression of other heat shock proteins was found to increase during the stringent response. Thus, the stringent response in E. coli induces expression of heat shock proteins. The requirements for this stringent induction of the heat shock proteins differ from those for temperature induction during the heat shock response.