GPN1 is a symbol for the gene, GPN-loop GTPase 1, in humans. Other names include: MBD2-interacting protein; MBDin; RNAPII-associated protein 4; XPA-binding protein 1; GPN-loop GTPase 1 ; RNA polymerase II associated protein 4; ATPBD1A; NTPBP; RPAP4; XAB1. The encoded protein is an enzyme with an amino acid length of 374 and a mass of 41.7 kDa. Other isoforms may exist. GPN1 is a member of the GPN-loop GTPase family. This gene shares homology with other species, including: Fly.