Guanine nucleotide exchange factor (GEF) for RAP1A, RAP1B and RAP2A small GTPases that is activated by binding cAMP. Seems not to activate RAB3A. Involved in cAMP-dependent, PKA-independent exocytosis through interaction with RIMS2. Interacts with RAP1B, RIMS1 and RIMS2. Probably part of a complex with RIMS2 and GTP-activated RAB3A. Expressed in cerebellum, pituitary, adrenal gland and liver. The N-terminal nucleotide phosphate binding region cAMP 1 has a much lower affinity for cAMP as compared to cAMP 2. The DEP domain is involved in membrane localization independent from regulation by cAMP. Produced by alternative promoter usage. Produced by alternative promoter usage. Produced by alternative splicing of isoform 1.