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

Abstract

ABSTRACTBorrelia 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. InB. burgdorferi, like many other bacterial species,ebfCis co-transcribed withdnaX, an essential component of the DNA polymerase III holoenzyme, which facilitates chromosomal replication. The expression of thednaX-ebfCoperon 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 ofdnaX-ebfCis controlled by direct interactions of DnaA, the chromosomal replication initiator, and EbfC at the unusually longdnaX-ebfC5’ 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 similarly impacted by ATP/ADP.In vitrostudies characterized DnaA as an activator ofdnaX-ebfCand EbfC as an anti-activator. We further found evidence that DnaA may regulate other genes essential for replication.IMPORTANCEThe dual-life cycle ofBorrelia burgdorferi, the causative agent of Lyme disease, is characterized by periods of rapid and slowed replication. The expression patterns of many of the spirochete’s virulence factors are impacted by these changes in replication rates. The connection between replication and virulence can be understood at thednaX-ebfCoperon. DnaX is a component of the DNA polymerase III holoenzyme that facilitates replication. EbfC is a nucleoid-associated protein that regulates the infection-associated outer surface Erp proteins, as well as other transcripts. The expression ofdnaX-ebfCis tied to replication rate, which we demonstrate is mediated by DnaA, the master chromosomal initiator protein and transcription factor, and EbfC.