title: Repression of aerobic leukotoxin transcription by integration host factor in Aggregatibacter actinomycetemcomitans.
abstract: Aggregatibacter actinomycetemcomitans has been implicated as the primary etiologic agent in localized aggressive periodontitis. This bacterium produces a leukotoxin which may help the bacterium evade the host immune response. Leukotoxin transcription is induced when A. actinomycetemcomitans is grown anaerobically, as in the periodontal pocket. Previously, a 35 bp oxygen-response-element (ORE) was shown to be responsible for oxygen regulation at the leukotoxin promoter. However, the gene's transcription is not controlled by Fnr or ArcA, the major oxygen regulators in other bacteria. To identify the potentially novel protein(s) that regulate leukotoxin transcription, protein extracts of A. actinomycetemcomitans were tested for ORE binding by mobility shift assays; one ORE-specific binding complex was found. Standard fractionation protocols and protein sequencing identified the ORE binding protein as integration host factor (IHF). DNaseI protection assays showed that the IHF binding site overlaps the first half of the ORE. To assess the effect of IHF on leukotoxin synthesis, an A. actinomycetemcomitans deletion mutant in ihfB was constructed and characterized. Interestingly, leukotoxin RNA and protein synthesis was de-repressed in the ihf mutant, although leukotoxin synthesis in still oxygen-regulated in the mutant cells. Thus, IHF plays a direct role in repressing leukotoxin transcription, but another protein is also involved in regulating leukotoxin expression in response to oxygen.
authors.affiliation: Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229-3900, USA. kolodrubetz@uthscsa.edu
authors.forename: David
authors.initials: D
authors.lastname: Kolodrubetz
authors.forename: Linda
authors.initials: L
authors.lastname: Phillips
authors.forename: Alex
authors.initials: A
authors.lastname: Burgum
mesh_terms: D000332:Aerobiosis; D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics* / Q000378:metabolism; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D004274:DNA, Recombinant; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D034982:Integration Host Factors / Q000235:genetics* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012329:RNA, Bacterial; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004274:DNA, Recombinant; D034982:Integration Host Factors; D012329:RNA, Bacterial