Influence of L-leucine and L-alanine on Lrp regulation of foo, coding for F1651, a pap homologue

The foo operon encodes F165(1) fimbriae that belong to the P-regulatory family and are synthesized by septicemic Escherichia coli. Using an Lrp-deficient host and the lrp gene cloned under the arabinose pBAD promoter, we demonstrated that foo was transcribed proportionally to the amount of Lrp synthesized. L-Leucine And L-alanine decreased drastically the steady-state transcription of foo and modified phase variation, independently of the presence of Fool. Specific mutations in the C-terminal region of Lrp reduced or abolished the repressive effect of these amino acids, indicating that they modulate F165(1) by affecting Lrp.