Borrelia burgdorferiDnaA and the nucleoid-associated protein EbfC coordinate expression of thednaX-ebfCoperon

Abstract

Borrelia burgdorferi, the spirochete agent of Lyme disease, has evolved within a consistent infectious cycle between tick and vertebrate hosts. The transmission of the pathogen from tick to vertebrate is characterized by rapid replication and a change in the outer surface protein profile. EbfC, a highly conserved nucleoid-associated protein, binds throughout the borrelial genome affecting expression of many genes, including the Erp outer surface proteins. In B. burgdorferi, like many other bacterial species, ebfC is co-transcribed with dnaX, an essential component of the DNA polymerase III holoenzyme, which facilitates chromosomal replication. The expression of the dnaX-ebfC operon is tied to the spirochete's replication rate, but the underlying mechanism for this connection was unknown. In this work, we provide evidence that the expression of dnaX-ebfC is controlled by direct interactions of DnaA, the chromosomal replication initiator, and EbfC at the unusually long dnaX-ebfC 5' UTR region. Both proteins bind to the 5' UTR DNA, with EbfC also binding to the RNA. The DNA binding of DnaA to this region was not impacted by ATP or ADP. In vitro studies characterized DnaA as an activator of dnaX-ebfC and EbfC as an anti-activator. We further found evidence that DnaA may regulate other genes essential for replication.