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Journal of Bacteriology


We previously showed, using a single-copy papBAp-lac fusion (previously designated papBA-lac), that pyelonephritis-associated pili (pap) pilin gene transcription is subject to both phase variation and thermoreg- ulatory control mechanisms (L. B. Blyn, B. A. Braaten, C. A. White-Ziegler, D. H. Rolfson, and D. A. Low, EMBO J. 8:613-620, 1989). At 37°C, Escherichia coli strains carrying the papBAp-lac fusion displayed both Lac' and Lac- colony phenotypes. In contrast, at 23°C, colonies displayed a uniform Lac- phenotype, suggesting that pilin was not transcribed at this temperature. In this study, a strain carrying the papBAp-lac fusion was subjected to mini-TnlO (mTnlO) mutagenesis to isolate mutants that could initiate transcription of pilin at the nonpermissive temperature. Two classes of thermoregulatory mutants were identified in which the mTnlO mutation was linked to the mutant phenotype. Class I mutants displayed a phase variation phenotype at both 37°C and 23°C, whereas class II mutants displayed a uniform Lac' colony phenotype at both temperatures. Preliminary analysis of these mutants showed that the mTnlO insertions in the class I mutants were chromosomally located, whereas the mTnlO insertions in the class II mutants were located within the papBAp-lac fusion phage. Southern blot analysis of the class I mutants demonstrated that mTnlO was present in the same 5.9-kilobase Sall DNA fragment in each mutant. Two of the class I mTnlO mutations were mapped to approximately 23.4 min on the E. coli K-12 chromosome. The locus defined by the class I mTnlO mutations was designated tcp, for thermoregulatory control ofpap. Analysis of phase transition rates of the class I mutants showed that the phase-off (Lac-)> phase-on (Lac') transition rates were higher than those observed with the nonmutant E. coli strain.





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© 1990, American Society for Microbiology


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