Cryo-EM structure of D-family DNA polymerase in a ternary elongation mode

PolD is an archaeal replicative DNA polymerase that possesses an atypical catalytic core (two-barrel) that is only found in RNA polymerases. We have reported he individual crystal structures of each subunit of PolD (Sauguet et al. 2016) as well as the Cryo-EM structure of PolD in complex with DNA (Raia et al , 2019) and PCNA (a processivity factor) (Madru et al. 2020). So far, the structure of the ternary complex of PolD with an incoming nucleotide and a DNA or RNA primer across a DNA template has not yet been resolved (Elongation mode). Such a structure has been challenging to obtain with a wild type version of PolD due to the flexibility of the primer substrate in the protein, we therefore created two different PolD variants (each including a different set of mutations) that showed to stabilize the elongation mode of PolD. Resolving these structures would be crucial to understand the positioning of the nucleotide in such a DNA polymerase with a unique catalytic core fold.