The regulation of pyelonephritis-associated pill (pap) pflin gene transcription has been examined using two operons (pap-17 and pap-21) isolated from the pyelonephritogenic Escherichia coli strain C1212. DNA sequence analysis and E.coli minicell analysis were used to map two genes (papB and papl) within the pilin regulatory regions of both pap-17 and pap-21, and the protein products of these genes were identified. Pilin transcription, initiated at the papBA promoter, was monitored by constructing single copy operon fusions with lacZYA in E.coli K-12. Inocula- tion of E.coli (pap\u27-lac) strains onto solid M9 minimal medium containing glycerol and the Lac indicator X-gal (M9-Glycerol) yielded both Lac\u27 and Lac- colony phenotypes. The Lac\u27 (\u27phase on\u27) and Lac- (\u27phase off\u27) phenotypes were heritable since reinoculation of M9-Glycerol with bacteria picked from Lac\u27 colonies gave rise to a much higher fraction of Lac\u27 colonies than reinoculation of M9-Glycerol with bacteria picked from Lac- colonies. Measurement of phase transition rates for E.coli (pap17\u27-lac) inoculated onto M9-Gly- cerol showed that the Lac - -Lac+ transition frequency (1.57 x 10-4/cell/generation) was reduced 35-fold when cells were inoculated onto minimal medium containing glucose (M9-Glucose). However, the Lac+-Lac- transition frequency obtained using M9-Glycerol (2.60 x 10-2/cell/generation) was 1.4-fold lower compared to results obtained with M9-Glucose. In contrast, lowering the incubation temperature of E.coli (pap17\u27-lac) cultures from 37°C to 23\u27C caused all cells to shift to the Lac- state. Together, our results strongly indicate that pap pfli phase-variation is transcriptionally regulated and show that phase-variation is responsive to changes in the bacterial environment
