Replicative helicases of bacteria and eukaryotes distribute into two distinct groups of unrelated origin. The loading and the activation of replicative helicases onto DNA are critical steps that are strictly regulated to prevent the initiation of unforeseen replications or improper assembly of functional replisomes. Bidirectional replication initiated at the origin of replication of the chromosome is conditional on the recruitment and the loading of two replicative helicases, installed head to head at oriC to form a stable nucleoprotein platform on which the replication machinery will then be assembled to generate two processive replisomes moving outwards from oriC ( 1). Replicative helicases are essential enzymes that unwind double-stranded DNA in front of the replication fork in the three domains of life. It sheds light on the strategy employed by phage helicase loaders to hijack bacterial replicative helicases and may explain the recurrent domestication of dnaC/I through evolution in bacteria. Our work is the first step toward the understanding of the ancestral mode of loading of bacterial replicative helicases on DNA. VcDciA interacts with VcDnaB with a 3/6 stoichiometry and we show that a determinant residue, which discriminates DciA- and DnaC/I-helicases, is critical in vivo. We show that VcDnaB can load itself on DNA in vitro and that VcDciA stimulates this function, resulting in an increased DNA unwinding.
#ACID GIF TAB FREE#
As other bacterial replicative helicases, VcDnaB adopts a toroid-shaped homo-hexameric structure, but with a slightly open dynamic conformation in the free state. While the DciA structure from Vibrio cholerae shares no homology with DnaC, it reveals similarities with DnaA and DnaX, two proteins involved during replication initiation. Instead, they are proposed to rely on DciA, an ancestral protein unrelated to DnaC/I. However, most bacteria do not express either of these two proteins. Their loading depends on accessory proteins and in bacteria, DnaC and DnaI are well characterized loaders.
Replicative helicases are essential proteins that unwind DNA in front of replication forks.
0 kommentar(er)
