SPACING REQUIREMENTS FOR TRANSCRIPTION ACTIVATION BY ESCHERICHIA-COLIFNR PROTEIN

We cloned a consensus DNA site for the Escherichia coli FNR protein at different locations upstream of the E. coli melR promoter. FNR can ac tivate transcription initiation at the melR promoter when the FNR bind ing site is centered around 41, 61, 71, 82, and 92 bp upstream from th e transcription start, The SF73 positive control amino acid substituti on in FNR interfered with transcription activation by FNR in each case . In contrast, the GA85 positive control substitution reduced activati on only at the promoter, where the FNR binding site is 41 bp upstream of the transcript start. The SF73 substitution appears to identify an activating region of FNR that is important for transcription activatio n at promoters that differ in architecture. Experiments with oriented heterodimers showed that this activating region is functional in the u pstream subunit of the FNR dimer at the promoter,where FNR binds aroun d 41 bp from the transcript start and in the downstream subunit at the promoters where FNR binds farther upstream.