Use of a two-color genetic screen to identify a domain of the global regulator Lrp that is specifically required for pap phase variation

A two-color genetic screen was used to determine mutations in lrp and to examine the participation of Lrp in coordinating Pap phase variation. The amino acid replacements in Lrp at position 126, 133 or 134 had a negligible influence on ilvIH transcription but significantly minimized the rate of Pap phase variation. In vitro analyses suggested that the T134A and E133G Lrp variants sustained affinities for pap and ilvIH DNAs in a manner which is identical to those of wild-type Lrp.