Cloning and characterization of the Actinobacillus actinomycetemcomitans gene encoding a heat-shock protein 90 homologue

In a search for clones from a λgtl 1 expression library of Actinobacillus actinomycetemcomitans (Aa) genomic DNA that expressed epitopes from a 70-kDa iron-repressible membrane protein, we inadvertently identified clones that encoded a member of the 90-kDa heat-shock protein (HSP 90) family. The gene appears to encode a homologue of HtpG, as the nucleotide sequence has ∼70% identity with the Escherichia coli (Ec) and Vibrio fischeri htpG. Growth of an Aa htpG insertion mutant at 42°C was reduced to 50% of the parent strain, similar to an Ec htpG deletion mutant. These data suggest that Aa HtpG performs a function similar to Ec HtpG.