Catalyzes the conversion of GTP to GDP through hydrolysis of the gamma-phosphate bond in GTP (PubMed:23711155, PubMed:29915238, PubMed:37179472). Appears to have an intrinsic GTPase activity that is stimulated by ZC3H15/DFRP1 binding likely by increasing the affinity for the potassium ions (PubMed:23711155). When hydroxylated at C-3 of 'Lys-22' by JMJD7, may bind to RNA and play a role in translation (PubMed:19819225, PubMed:29915238). Binds to microtubules and promotes microtubule polymerization and stability that are required for mitotic spindle assembly during prophase to anaphase transition. GTPase activity is not necessary for these microtubule-related functions (PubMed:28855639). {ECO:0000269|PubMed:19819225, ECO:0000269|PubMed:23711155, ECO:0000269|PubMed:28855639, ECO:0000269|PubMed:29915238, ECO:0000269|PubMed:37179472}. This is the function of DRG1 (developmentally regulated GTP binding protein 1, Ensembl gene identifier ENSG00000185721).