The Bacterial Replicative Helicase Loader DciA is a DNA Condenser.

Abstract

The loading of the bacterial replicative helicase is an essential step for genome replication and depends on the assistance of accessory proteins. Several of these proteins have been identified across the bacterial phyla. DciA is the most common loading protein in bacteria, yet the one whose mechanism is the least understood. We have previously shown that VcDciA from Vibrio cholerae, composed of a globular KH-like domain followed by an unfolded extension, has a strong affinity for DNA. Here, we characterized the droplets formed by VcDciA upon interaction with a short single-stranded substrate. We demonstrate the fluidity of these droplets using light microscopy and address their network organization through electron microscopy, thereby bridging events to conclude on a liquid-liquid phase separation behavior. Additionally, we observe the recruitment of VcDnaB inside the VcDciA-DNA droplets. We show that DnaC from Escherichia coli is also competent to form these condensate structures in the presence of ssDNA. Our data open up possibilities for the involvement of DciA in the formation of non-membrane compartments within the bacterium, facilitating the assembly of replication players with the chromosomal DNA.