Small GTPase required for proper nuclear import of RNA polymerase II (RNAPII) (PubMed:20855544, PubMed:21844196). May act at an RNAP assembly step prior to nuclear import (PubMed:23267056). Promotes sister chromatid separation during anaphase (PubMed:21532343). Heterodimers with GPN2 or GPN3 (PubMed:23324351, PubMed:23267056). Binds to RNA polymerase II (RNAPII) in a GTP-dependent manner (PubMed:20855544, PubMed:21844196). Interacts with nuclear pore protein NUP133 and nuclear export factor CRM1 (PubMed:21844196). Interacts with PCL1 (PubMed:15082539). Phosphorylated by the cyclin-CDK PCL1-PHO85. Present with 15200 molecules/cell in log phase SD medium. Belongs to the GPN-loop GTPase family.