PROMOTERS AND TRANSCRIPTS ASSOCIATED WITH THE AROP GENE OF ESCHERICHIA-COLI

Analysis of in vitro transcriptional events initiating within the regi on immediately upstream of the aroP coding region has revealed the pre sence of three promoters, P1, P2, and P3. Both P1 and P2 give rise to mRNA encoding the AroP protein, whereas P3 initiates transcription in the opposite direction. Both P1 and P3 contain UP elements which contr ibute to promoter strength. Regulation of expression from these three promoters has been examined in vitro by using supercoiled DNA template s and in vivo by using lacZ transcriptional fusions and specific promo ter mutants. Expression from P2 is partially repressed by TyrR alone b oth in vitro and in vivo. Addition of the aromatic amino acid tyrosine , phenylalanine, or tryptophan further increases this repression. P1 i s not repressed by TyrR alone but is repressed in vivo in the presence of phenylalanine, tyrosine, or tryptophan. This also occurs in vitro but requires Ca2+ ions in the reaction mixture for its demonstration. Under these conditions, transcription from P3 is enhanced by TyrR prot ein with phenylalanine, tyrosine, or tryptophan. However, we were unab le to demonstrate P3 expression in vivo. Under repressing conditions, there is no production of truncated RNA molecules (from P1), which wou ld be expected if repression involved a roadblock mechanism.