DNA looping-dependent autorepression of LEE1 P1 promoters by Ler in enteropathogenic Escherichia coli (EPEC)

Ler [locus of enterocyte effacement (LEE)-encoded regulator], encoded by the first gene of the LEE1 operon in enteropathogenic Escherichia coli (EPEC), represses its own transcription driven by two promoters separated by 10 bp. We found that Ler does this repression through a DNA loop of 16 helical turns, in which RNA polymerase is trapped as open promoter complex, although this complex should be most readily transformed into productive initiation complex.