Catalyzes the condensation of the acetyl group of acetyl-CoA with oxaloacetate to form citrate. acetyl-CoA + H2O + oxaloacetate = citrate + CoA + H(+) Inhibited by p-hydroxymercuribenzoate and EDTA. Homotetramer. Expressed under all growth conditions. Belongs to the alpha-IPM synthase/homocitrate synthase family.