The function of ENSG00000138073 (PREB, prolactin regulatory element binding) is as follows. Guanine nucleotide exchange factor (GEF) that regulates the assembly of the coat protein complex II/COPII in endoplasmic reticulum (ER) to Golgi vesicle-mediated transport. Selectively activates SAR1A and SAR1B by promoting the exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP) in these small GTPases (PubMed:32358066). In their activated GTP-bound state, SAR1A and SAR1B insert into the membrane of the endoplasmic reticulum where they recruit the remainder of the coat protein complex II/COPII which is responsible for both the sorting of proteins and the deformation and budding of membranes into vesicles destined to the Golgi (PubMed:32358066). . Was first identified based on its probable role in the regulation of pituitary gene transcription. Binds to the prolactin gene (PRL) promoter and seems to activate transcription. .