The function of Ensembl gene identifier ENSG00000198522 (GPN1, GPN-loop GTPase 1) is as follows. Small GTPase involved in the correct assembly of RNA polymerase II (RNAPII) complex, ensuring proper nuclear import of RNAPII (PubMed:11058119, PubMed:20855544, PubMed:21768307, PubMed:28153773). In vitro, exhibits a chaperone-like activity and a chaperone substrate protein can stimulate its GTPase activity. It is proposed to bind exposed hydrophobic peptide regions of newly synthesized RNAP II subunit, triggering the opening of a hydrophobic pocket in its GDP-bound state. This interaction likely traps exposed hydrophobic regions, preventing misassembly and providing a time window for association with the cognate RNAP II subunit. Peptide binding promotes GDP release, and increasing GTP affinity to facilitate GTP rebinding. Subsequent GTP hydrolysis would then lead to the release of the bound RNAP II subunit to enable association with cognate subunits and RNAP II assembly (By similarity). Forms an interface between the RNA polymerase II enzyme and chaperone/scaffolding proteins, suggesting that it is required to connect RNA polymerase II to regulators of protein complex formation (PubMed:17643375). May be involved in nuclear localization of XPA (PubMed:11058119). {ECO:0000250|UniProtKB:P47122, ECO:0000269|PubMed:11058119, ECO:0000269|PubMed:17643375, ECO:0000269|PubMed:20855544, ECO:0000269|PubMed:21768307, ECO:0000269|PubMed:28153773}.