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We previously showed that theAggregatibacter actinomycetemcomitans lsrACDBFG andlsrRK operons are regulated by LsrR and cyclic AMP receptor protein (CRP) and that proper regulation of thelsr locus is required for optimal biofilm growth byA. actinomycetemcomitans . Here, we identified sequences that reside immediately upstream from both thelsrA andlsrR start codons that closely resemble the consensus recognition sequence ofEscherichia coli integration host factor (IHF) protein.A. actinomycetemcomitans IHFα and IHFβ were expressed and purified as hexahistidine fusion proteins, and using electrophoretic mobility shift assays (EMSAs), the IHFα-IHFβ protein complex was shown to bind to probes containing the putative IHF recognition sequences. In addition, single-copy chromosomal insertions oflsrR promoter-lacZ andlsrA promoter-lacZ transcriptional fusions in wild-typeA. actinomycetemcomitans and ΔihfA and ΔihfB mutant strains showed that IHF differentially regulates thelsr locus and functions as a negative regulator oflsrRK and a positive regulator oflsrACDBFG . Deletion ofihfA orihfB also reduced biofilm formation and altered biofilm architecture relative to the wild-type strain, and these phenotypes were partially complemented by a plasmid-borne copy ofihfA orihfB . Finally, using 5′ rapid amplification of cDNA ends (RACE), two transcriptional start sites (TSSs) and two putative promoters were identified forlsrRK and three TSSs and putative promoters were identified forlsrACDBFG . The function of the twolsrRK promoters and the positive regulatory role of IHF in regulatinglsrACDBFG expression were confirmed with a series oflacZ transcriptional fusion constructs. Together, our results highlight the complex transcriptional regulation of thelsrACDBFG andlsrRK operons and suggest that multiple promoters and the architecture of thelsrACDBFG-lsrRK intergenic region may control the expression of these operons.

journal of bacteriology

Differential Transcriptional Regulation of Aggregatibacter actinomycetemcomitans <i>lsrACDBFG</i> and <i>lsrRK</i> Operons by Integration Host Factor Protein

Differential Transcriptional Regulation of Aggregatibacter actinomycetemcomitans lsrACDBFG and lsrRK Operons by Integration Host Factor Protein