The function of Ensembl gene identifier ENSG00000156313 (RPGR, retinitis pigmentosa GTPase regulator) is as follows. Acts as a guanine-nucleotide releasing factor (GEF) for RAB8A and RAB37 by promoting the conversion of inactive RAB-GDP to the active form RAB-GTP (PubMed:20631154). GEF activity towards RAB8A may facilitate ciliary trafficking by modulating ciliary intracellular localization of RAB8A (PubMed:20631154). GEF activity towards RAB37 maintains autophagic homeostasis and retinal function (By similarity). Involved in photoreceptor integrity (By similarity). May control cilia formation by regulating actin stress filaments and cell contractility. May be involved in microtubule organization and regulation of transport in primary cilia (PubMed:21933838). May play a critical role in spermatogenesis and in intraflagellar transport processes (By similarity). {ECO:0000250|UniProtKB:Q9R0X5, ECO:0000269|PubMed:20631154, ECO:0000269|PubMed:21933838}.