The TyrR protein of Escherichia coli is a class I transcription activator

In vitro transcription studies reveal that phenylation and purified TyrR exhibit capacity to activate the in vitro transcription from the tyrP promoter of Escherichia coli by wild-type RNA polymerase. This activation involves a specific interaction between RNA polymerase and TyrR protein. A putative promoter is present in the strand opposite to tyrP and within the TyrR-binding region. Absence of TyrR-mediated activation in the mutant alpha 235 RNA polymerase reveals TyrR as a class I transcription activator.