Crystal structure of the 3’→5’ exonuclease from Methanocaldococcus jannaschii

RecJ exonucleases are members of the DHH phosphodiesterase family ancestors of eukaryotic Cdc45, the key component of the CMG (Cdc45–MCM–GINS) complex at the replication fork. They are involved in DNA replication and repair, RNA maturation and Okazaki fragment degradation. Bacterial RecJs resect 5′-end ssDNA. Conversely, archaeal RecJs are more versatile being able to hydrolyse in both directions and acting on ssDNA as well as on RNA. In Methanocaldococcus jannaschii two RecJs were previously characterized: RecJ1 is a 5’→3′ DNA exonuclease, MjaRecJ2 works only on 3′-end DNA/RNA with a preference for RNA.Here, I present the crystal structure of MjaRecJ2, solved at a resolution of 2.8 Å, compare it with the other RecJ structures, in particular the 5’→3’ TkoGAN and the bidirectional PfuRecJ, and discuss its characteristics in light of the more recent knowledge on RecJs.This work adds new structural data that might improve the knowledge of these class of proteins.