TheStreptococcus pneumoniae ciaRegulon: CiaR Target Sites and Transcription Profile Analysis

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Abstract
TheciaR-ciaHsystem is one of 13 two-component signal-transducing systems of the human pathogenStreptococcus pneumoniae. Mutations in the histidine protein kinase CiaH confer increased resistance to beta-lactam antibiotics and interfere with the development of genetic competence. In order to identify the genes controlled by theciasystem, theciaregulon, DNA fragments targeted by the response regulator CiaR were isolated from restricted chromosomal DNA using the solid-phase DNA binding assay and analyzed by hybridization to an oligonucleotide microarray representing theS. pneumoniaegenome. A set of 18 chromosomal regions containing 26 CiaR target sites were detected and proposed to represent the minimalciaregulon. The putative CiaR target loci included genes important for the synthesis and modification of cell wall polymers, peptide pheromone and bacteriocin production, and thehtrA-spo0Jregion. In addition, the transcription profile ofcialoss-of-function mutants and those with an apparent activatedciasystem representing the off and on states of the regulatory system were analyzed. The transcript analysis confirmed thecia-dependent expression of seven putative target loci and revealed three additionalcia-regulated loci. Five putative target regions were silent under all conditions, and for the remaining three regions, nocia-dependent expression could be detected. Furthermore, the competence regulon, including thecomCDEoperon required for induction of competence, was completely repressed by theciasystem.

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