One of the goals of the research in the field of cell biology is the understanding of the physiology of intracellular membrane trafficking. In this respect, the present study is aimed at the comprehension of the molecular mechanisms that govern membrane trafficking, with emphasis at the events that occur at the level of the Golgi complex. Fundamental insights into the organization and the function of the Golgi complex have been provided by the use of pharmacological agents. Studies on the effects of Brefeldin A (BFA), a fungal toxin that potently inhibits membrane traffic and causes an extremely rapid disruption of the Golgi architecture and function, led to the identification of a 50-kDa cytosolic substrate of BFA-induced-ADP-ribosylation (BARS) and several lines of evidence indicated BARS as a possible regulator of the structure and function of the Golgi complex. In order to understand the molecular mechanisms that regulate the Golgi organization, the identification and characterization of BARS was undertaken. In this thesis the cloning and sequence analysis of BARS is reported, together with its functional characterization. BARS is shown to belong to the CtBP family of proteins and thus renamed CtBP3/BARS. It induces membrane fission of the Golgi tubules in vitro and catalyses the conversion of lysophosphatidic acid (LPA) into phosphatidic acid (PA), a reaction that appears essential for membrane fission at the Golgi complex as well as at the plasma membrane. This study also shows that CtBP3/BARS is localized on the Golgi and other cellular membranes. The identification of molecular interactors of CtBP3/BARS is also reported and their possible roles in membrane fission discussed.