Guanine nucleotide exchange factor (GEF) which may activate RAB6A and RAB39A and/or RAB39B. Promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form (By similarity). Involved in the negative regulation of neurite outgrowth (By similarity). Interacts with RAB6A bound to GTP. Belongs to the RAB6IP1 family.