Members of the RAB protein family, such as RAB1B, are low molecular mass monomeric GTPases localized on the cytoplasmic surfaces of distinct membrane-bound organelles. RAB1B functions in the early secretory pathway and is essential for vesicle transport between the endoplasmic reticulum (ER) and Golgi (Chen et al., 1997 [PubMed 9030196]; Alvarez et al., 2003 [PubMed 12802079]).[supplied by OMIM, Jan 2009],function:Protein transport. Regulates vesicular transport between the endoplasmic reticulum and successive Golgi compartments.,miscellaneous:Rab-1B binds GTP and GDP and possesses intrinsic GTPase activity.,PTM:Prenylated; by GGTase II, only after interaction of the substrate with Rab escort protein 1 (REP1).,similarity:Belongs to the small GTPase superfamily. Rab family.,subcellular location:Targeted by REP1 to membranes of specific subcellular compartments including endoplasmic reticulum, Golgi apparatus, and intermediate vesicles between these two compartments. In the GDP-form, colocalizes with GDI in the cytoplasm.,subunit:Interacts with MICAL1, MICAL2 and MICAL3. Interacts with GDI1; the interaction requires the GDP-bound state. Interacts with CHM/REP1; the interaction requires the GDP-bound form and is necessary for prenylation by GGTase II.,