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Transcriptional activation of a pap pilus virulence operon from uropathogenic Escherichia coli
Insights
Researchers investigated the regulation of pili synthesis in uropathogenic Escherichia coli. They discovered that papB and papI genes control the expression of the major pilus subunit gene, papA, influencing bacterial adhesion.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Uropathogenic Escherichia coli (UPEC) utilizes pili for adhesion to host tissues, a critical step in urinary tract infections.
- Understanding the genetic regulation of pilus synthesis is crucial for developing targeted therapeutic strategies against UPEC infections.
Purpose of the Study:
- To analyze the gene cluster responsible for pili production in UPEC.
- To elucidate the regulatory mechanisms governing the synthesis of the major pilus subunit, papA.
- To investigate the roles of papB and papI genes in pili gene expression.
Main Methods:
- Nucleotide sequencing of the papI-papB-papA gene region.
- Transcriptional analysis using Northern blotting and lacZ operon fusions.
- Investigating gene expression dependence on cAMP and its receptor protein (CRP).
Main Results:
- Identified two cistrons, papB and papI, upstream of the papA gene, regulating pili synthesis.
- papB encodes a trans-acting factor essential for papA transcription, while papI stimulates papB transcription.
- papA expression is cis-dependent on the papI-papB region, and papB transcription requires cAMP-CRP complex binding upstream of its promoter.
Conclusions:
- The papI-papB-papA gene cluster exhibits complex transcriptional regulation involving both trans-acting factors and cis-acting elements.
- The cAMP-CRP system plays a significant role in controlling papB transcription, indirectly affecting pilus production.
- This study provides insights into the molecular mechanisms underlying UPEC pilus biogenesis and regulation.
Abstract:
A gene cluster mediating production of pili in uropathogenic Escherichia coli was analysed with respect to regulation of pili synthesis. Two cistrons, papB and papI, were localized upstream of the major pilus subunit gene, papA. The papI-papB-papA region was characterized by nucleotide sequencing and by transcriptional analysis. The papA gene was primarily represented by an 800 nucleotide long transcript but was also co-transcribed with papB as a less abundant 1300 nucleotide long mRNA. Both transcripts presumably terminated at the same site downstream of the papA coding sequence. The weakly expressed papI gene was transcribed in the opposite direction to that of papB and papA. Studies with lacZ operon fusions showed that the papB gene encoded a trans-active effector required for papA transcription. Similarly, the papI gene stimulated papB transcription in trans. Furthermore, full expression of papA was cis dependent upon the papI-papB region. Transcription of the papB gene was shown to be dependent upon cAMP and its receptor protein. A binding site for the cAMP-CRP complex was postulated in the DNA sequence upstream of the papB promoter.