Regulation of uropathogenic Escherichia coli adhesin expression by DNA methylation

Pap pili play an important role in the pathogenesis of upper urinary tract infections by enabling uropathogenic Escherichia coli to adhere to host epi thelial cells. Pap pili are coded for by the pyelonephritis-associated pili (pap) operon, which consists of 11 genes required for the expression and a ssembly of Pap pill. Expression of Pap pill is regulated by a phase variati on mechanism in which the pili expression state of the bacterial population is skewed between phase-on (expression positive) and phase-off (expression negative) states. Pap phase variation is controlled by the cooperative bin ding of leucine-responsive regulatory protein (Lrp) to two sets of Lrp bind ing sites in the upstream regulatory region of the pop operon. A single GAT C sequence, which is the target site for deoxyadenosine methylase (Dam), is centrally located within each Lrp binding region. Dam plays a critical rol e in the expression of Pap pill via the formation of DNA methylation patter ns. Methylation of GATC-I reduced the affinity of Lrp for pop DNA by about twofold, Conversely, Lrp specifically blocked methylation of pop GATC-I in vitro. These data support the hypothesis that Lrp and Dam compete for bindi ng to GATC-I, and are consistent with previous results indicating that meth ylation of GATC-I is important for stability of the phase-off state. (C) 19 98 Academic Press.