RecG protein: Difference between revisions

Domain 1 of RecG contacts with DNA at the junction itself, indicating the specificity of the interaction with stalled replication forks. The junction is hold by the greek key motif on one side and an extended  β hairpin (residues 259–266) on another. The template strands interact with the protein grooves that are too small to accommodate DNA duplex, resulting in simultaneous split of the leading and the lagging strands. The breaking of the leading strand and the lagging strand duplexes is stabilized by the aromatic ring of Phe 204 and Tyr 208 of the protein, respectively. This mimicks base stacking of a duplex DNA structure. One of the DNA bases doesn’t contact with RecG, serving as a transient state to facilitate flipping between the duplexes during junction migration.

Additionally, the phosphodiester backbones of the duplex arms of the junction are interacting with Domain 1 and 3 of RecG. The interaction allows the formation of either a B-form (DNA) or an A-form duplex (DNA/RNA), what explains why RecG can unwind Holliday junctions (DNA) as well as R-loops (RNA)<ref name="structure" />.

'''FUNCTION''' [[Image:Manganon2.jpg | thumb ]]

RecG is an enzyme with helicase, translocase and ATPase activity. It binds to a stalled replication fork and converts it into a holliday junction, which can be resolved  later by RuvC.

RecG binds initially to the junction with the arms of the fork located at domain 1 of the protein. The orphan base pairs are stabilized by aromatic interactions with the protein. In order to unwind both arms simultaneously, the protein drags the junction across the wedge domain (residues 154–252). Due to steric interference only the template strands on the leading and lagging arms would be able to pass through the grooves on either side of the wedge domain. Therefore, the newly synthetized strands are stripped off the template, but their proximity allows association of these complementary strands to form a four-way junction. This translocation is driven by a repetitive opening and closing of the cleft between Domains 2 and 3 as ATP binds and hydrolyzes, allowing the protein alternately to bind and release the template duplex region, thereby walking along the DNA<ref name="structure" />.