Identification and characterization of an archaeal nucleoid-associated protein that binds an essential motif in DNA replication origins.

DNA replication is a process fundamental to the propagation of all cellular life on the planet. Replication typically has defined start sites, replication origins, and these are designated by their recognition by specific initiator proteins. In addition to initiators, general chromatin or nucleoid-associated proteins have been shown to play roles in modulating origin efficiency in eukaryotes and bacteria. To date, nothing is known about the role of chromatin proteins in origin function in the archaeal domain of life. In the current work, we describe a dissection of sequences elements required for in vivo function of an archaeal DNA replication origin. Our data demonstrate the essential nature of a hitherto uncharacterized sequence element, the ucm. We identify the protein, UBP, that interacts with the ucm and describe a series of data derived from in vivo and in vitro experiments that characterize the role of UBP at the molecular and structural levels. Taken together, our data provide evidence that UBP functions as a general nucleoid-associated protein that plays a key role in facilitating the egress of the MCM replicative helicase from DNA replication origins.