Evidence for a methylation-blocking factor (mbf) locus involved in pap pilus expression and phase variation in Escherichia coli.

摘要: Transcription of the pyelonephritis-associated pilus (pap) operon Escherichia coli is subject to regulation by a phase variation control mechanism in which pap pilin gene alternates between transcriptionally active (phase-on) and inactive (phase-off) states. Pap appears involve differential inhibition deoxyadenosine methylase (Dam) methylation two GATC sites, GATC1028 GATC1130, located regulatory region upstream papBA promoter. DNA from phase-on cells contains an unmethylated adenosine site, whereas phase-off GATC1130 site. papI papB are genes operon. Analysis deletion mutants suggests that required for at site; however, neither nor We have identified chromosomal locus, mbf (methylation-blocking factor), protection both sites. The locus was after transposon mTn10 mutagenesis mapped 19.6 min on E. chromosome. effect mutations within transcription determined using papBAp-lac fusion places lacZ under containing mbf::mTn10 mbf+ expressed beta-galactosidase levels about 30-fold lower than level measured cells. These results indicated necessary were supported Northern (RNA) blotting primer extension analyses. Moreover, insertion greatly reduced expression. isolated low-copy-number cosmid, pMBF1. Complementation analysis each seven contained same or identification transcription, supports hypothesis controlled involving alternation different