The RUN domain, named after RPIP8, unc-14 and NESCA, is organised into six conserved blocks (A-F), which are predicted to constitute the 'core' of a globular structure tolerating insertions of considerable length between the conserved blocks. The RUN domain is found in one or two copies in several proteins that are linked particularly to the functions of GTPases in the Rap and Rab families. RUN domains can be associated with TBC/rab GAP, FYVE, DENN, SH3, DAG/PE-binding, PLAT/LH2, PH or PX domains. The RUN domain may have a role in the interaction of various proteins with cytoskeletal filaments PMID:11509568.