Identification and characterization of BpH2, a novel histone H1 homolog in Bordetella pertussis

Abstract

A basic protein, BpH2, with an apparent molecular mass of 18 kDa was purified from Bordetella pertussis, and the corresponding gene, bph2, was cloned. Sequence analysis revealed some homology to the H1 class of eukaryotic histones and to AlgP protein of Pseudomonas aeruginosa. BpH2 binds both single-and double-stranded DNA in a nonspecific manner. Deletion of the corresponding gene in B. pertussis generated a BpH2 null mutant with an altered growth rate in which the expression of two virulence factors, adenylate cyclase-hemolysin (CyaA) and filamentous hemagglutinin (FhaB), was reduced. It is suggested that BpH2 may exhibit specific regulatory functions through its interaction with chromosomal DNA.Eubacteria maintain their DNA in a negatively supercoiled form, achieved by DNA topoisomerase and by architectural elements called histone-like proteins. Among these, the best characterized are HU, HNS, and IHF (10,20,24). These chromatin-associated proteins organize the bacterial chromosome and also exert regulatory influence on transcription, recombination, and DNA replication (11,20,30,35). For many pathogenic bacteria, it has been suggested that the expression of certain virulence genes, which are regulated by a specific regulatory element, can also be affected by DNA topology (9). In line with this hypothesis, a new class of chromatin-associated proteins which present homology with the eukaryotic histone H1 protein have been found in some pathogenic bacteria. These proteins include the Hc1 and Hc2 proteins of Chlamydia species (15,16,23) and the AlgP protein of Pseudomonas aeruginosa (8). It has been established that AlgP is involved in the regulation of the algD gene, which plays a key role in mucoidy, necessary for virulence of this bacterium (7,8,17). Recently, Scarlato et al. (29) have identified and characterized BpH1, a new member of the family with homology to histone H1 which is involved in chromatin formation in Bordetella pertussis (29). B. pertussis, the etiological agent of whooping cough, encodes a large number of virulence factors, including pertussis toxin (Ptx), filamentous hemagglutinin (FhaB), and adenylate cyclase-hemolysin (CyaA) (6, 36). The expression of virulence factors in Bordetella species is coordinately regulated by the bvg locus, which encodes two proteins, BvgA and BvgS, members of the histidine-kinase response regulator family of signal transduction systems (2,26,33). Mutations in the bvg locus abolish the expression of virulence factors and result in avirulent-phase bacteria.In the present paper, I report the identification of a second protein of B. pertussis, with homology to eukaryotic histone H1 protein, named BpH2. The bph2 gene has been sequenced, and the deduced amino acid sequence showed homology with eukaryotic histone H1 proteins and AlgP of P. aeruginosa. The BpH2 protein was purified, and its interaction with DNA in vitro was analyzed. A B. pertussis strain lacking the bph2 gene was constructed, and the effects of the deletion on growth rate and on the expression of two v...

Insights into a dinoflagellate genome through expressed sequence tag analysis

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