rRNA antitermination functions with heat shock promoters

Transcription antitermination in the rRNA operons of Escherichia coli requires a unique nucleic acid sequence that serves as a signal for modification of the elongating RNA polymerase, making it resistant to Rho-dependent termination. We examined the antitermination ability of RNA polymerase elongation complexes that had initiated at three different heat shock promoters, dnaK, groE, and clpB, and then transcribed the antitermination sequence to read through a Rho-dependent terminator. Terminator bypass comparable to that seen with sigma(70) promoters was obtained. Lack of or inversion of the sequence abolished terminator readthrough. We conclude that RNA polymerase that uses sigma(32) to initiate transcription can adopt a conformation similar to that of sigma(70)-containing RNA polymerase, enabling it to interact with auxiliary modifying proteins and bypass Rho-dependent terminators.