IN-VITRO TRANSCRIPTIONAL ANALYSIS OF TYRR-MEDIATED ACTIVATION OF THE MTR AND TYRP-COLI(3 PROMOTERS OF ESCHERICHIA)

In order to understand the mechanism by which the TyrR protein activat es transcription from the mtr and tyrP+3 promoters, we have carried ou t in vitro transcription experiments with supercoiled DNA templates. W e have shown that addition of the histone-like protein HU or integrati on host factor (IHF) greatly inhibited the transcription from the mtr and tyrP+3 promoters. In the presence of phenylalanine, the wild-type TyrR protein, but not a mutant TyrR protein (activation negative), was able to relieve the HU- or IHF-mediated inhibition of transcription. In contrast, the alleviation of the HU- or IHF-mediated transcription inhibition by the wild-type TyrR protein did not occur when a mutant R NA polymerase with a C-terminally truncated alpha subunit was used to carry out the transcription reaction.