GTPase which can activate the MEK/ERK pathway and induce cell transformation when overexpressed. May act as a nuclear scaffold for MAPK1, probably by association with MAPK1 nuclear export signal leading to enhanced ERK1/ERK2 signaling. Interacts directly with MAPK1 (wild-type and kinase-deficient forms). Interacts directly (in GTP-bound form) with MAP2K1 (wild-type and kinase-deficient forms). Overexpressed in gastrointestinal cancers; expression correlates with later tumor-node-metastasis stages of colorectal cancers. DNAJC27/RBJ knockdown in several colorectal cancer cell lines is correlated to inhibition of MEK/ERK activation, cell proliferation, colony formation and in vivo tumor growth. Belongs to the small GTPase superfamily. Rab family.