Small GTPase-like component of the intraflagellar transport (IFT) complex B that promotes the exit of the BBSome complex from cilia via its interaction with ARL6 (PubMed:25446516). Not involved in entry of the BBSome complex into cilium. Prevents aggregation of GTP-free ARL6. Required for hedgehog signaling (PubMed:25446516). Forms a subcomplex within the IFT complex B with IFT25 (By similarity). Its role in intraflagellar transport is mainly seen in tissues rich in ciliated cells such as kidney and testis. Essential for male fertility, spermiogenesis and sperm flagella formation (PubMed:28964737). Plays a role in the early development of the kidney (PubMed:29626631). May be involved in the regulation of ureteric bud initiation (PubMed:29626631). Component of the IFT complex B, at least composed of IFT20, IFT22, HSPB11/IFT25, IFT27, IFT46, IFT52, TRAF3IP1/IFT54, IFT57, IFT74, IFT80, IFT81, and IFT88 (PubMed:19253336). Interacts with HSPB11/IFT25 (PubMed:28430876). Interacts with TTC30B (PubMed:23810713). Interacts with RABL2/RABL2A; binding is equal in the presence of GTP or GDP (PubMed:23055941). Interacts with IFT88 (PubMed:19253336). Interacts with ARL6; recognizes and binds with the GTP-free form of ARL6 (By similarity). Localizes to the sperm flagellum. Expressed predominantly in the testis (at protein level) (PubMed:28964737). Co-localizes with RABL2/RABL2A in the midpiece of elongated spermatids within the testis (at protein level). Null mutants retain the ability to ciliate and survive through gestation. They die shortly after birth due to different phenotypes reminiscent of Shh signaling defects: polydactyly, lung isomerisms, and structural heart defects (PubMed:25446516). Conditional knockout in male germ cells results in infertility, abnormal sperm morphology, significantly reduced sperm count and sperm mobility (PubMed:28964737). Mutant mice with germline deletion of IFT27 die shortly after birth with structural defects in most organs including the kidneys, where duplicated collecting duct system and/or duplex kidney is often observed. Conditional deletion in the collecting duct results in smaller kidneys that develop only mild tubule dilation with age whereas conditional deletion from the peri-Wolffian duct stroma results in duplex kidneys (PubMed:29626631). Belongs to the small GTPase superfamily. Rab family.