Leucine‐responsive regulatory protein, IS <i>1</i> insertions, and the negative regulator FaeA control the expression of the <i>fae</i> (K88) operon in <i>Escherichia coli</i>

Abstract

Nucleotide sequence analysis of the fae operon encoding the biosynthesis of K88 fimbriae revealed the presence of two divergently transcribed regulatory genes, faeA and faeB, separated by two inverted IS1 insertions. The amino acid sequences of the regulatory proteins FaeA and FaeB show similarity to the primary structure of corresponding regulatory proteins involved in the biosynthesis of Pap and S fimbriae. Expression of faeA is positively controlled by the FaeA protein, whereas K88 fimbriae production is negatively controlled by the co-operative activity of FaeA and the leucine-responsive regulatory protein (Lrp). Exchange of FaeA for Papl, a positive regulator of Pap fimbriae expression, also represses K88 production indicating that the combination Papl/Lrp has opposite effects on fae and pap expression. Mutations in faeB had no effect on the biosynthesis of K88 fimbriae. The presence of the two IS1 insertions is hypothesized to neutralize part of the repression of K88 biosynthesis by FaeA/Lrp. Like pap, the fae operon does not respond to exogenous leucine.