DNA-Binding Properties of YbaB, a Putative Nucleoid-Associated Protein From Caulobacter crescentus

Nucleoid-associated proteins (NAPs) or histone-like proteins (HLPs) are DNA-binding proteins present in bacteria that play an important role in nucleoid architecture and gene regulation. NAPs affect bacterial nucleoid organization via DNA bending, bridging, or forming aggregates. EbfC is a nucleoid-associated protein identified first in Borrelia burgdorferi, belonging to YbaB/EbfC family of NAPs capable of binding and altering DNA conformation. YbaB, an ortholog of EbfC found in Escherichia coli and Haemophilus influenzae, also acts as a transcriptional regulator. YbaB has a novel tweezer-like structure and binds DNA as homodimers. The homologs of YbaB are found in almost all bacterial species, suggesting a conserved function, yet the physiological role of YbaB protein in many bacteria is not well understood. In this study, we characterized the YbaB/EbfC family DNA-binding protein in Caulobacter crescentus. C. crescentus has one YbaB/EbfC family gene annotated in the genome (YbaB ) and it shares 41% sequence identity with YbaB/EbfC family NAPs. Computational modeling revealed tweezer-like structure of YbaB , a characteristic of YbaB/EbfC family of NAPs. N-terminal-CFP tagged YbaB localized with the nucleoid and is able to compact DNA. Unlike B. burgdorferi EbfC protein, YbaB protein is a non-specific DNA-binding protein in C. crescentus. Moreover, YbaB shields DNA against enzymatic degradation. Collectively, our findings reveal that YbaB is a small histone-like protein and may play a role in bacterial chromosome structuring and gene regulation in C. crescentus.