Methylation patterns in pap regulatory DNA control pyelonephritis-associated pili phase variation in E. coli

Abstract We have examined the roles of pap DNA methylation patterns in the regulation of the switch between phase ON and OFF pyelonephritis-associated pili (Pap) expression states in E. coli. Two Dam methyltransferase sites, GATC 1028 and GATC 1130 , were shown previously to be differentially methylated in phase ON versus phase OFF cells. In work presented here, these sites were mutated so that they could not be methylated, and the effects of these mutations on Pap phase variation were examined. Our results show that methylation of GATC 1028 blocks formation of the ON state by inhibiting the binding of Lrp and Papl regulatory proteins to this site. Conversely, methylation of GATC 1130 is required for the ON state. Evidence indicates that this occurs by the inhibition of binding of Lrp to sites overlapping the pilin promoter. A model describing how the transition between the phase ON and OFF methylation states might occur is presented.