The phosphoenolpyruvate-dependent sugar phosphotransferase system (sugar PTS), a major carbohydrate active transport system, catalyzes the phosphorylation of incoming sugar substrates concomitantly with their translocation across the cell membrane. The enzyme II LacEF PTS system is involved in lactose transport. Binds 1 Mg(2+) ion per trimer. Homotrimer. By lactose. The operon consists of lacABCDFEGX. A second transcript of only lacF and lacE is also lactose-induced. The PTS EIIA type-3 domain is phosphorylated by phospho-HPr on a histidyl residue. Then, it transfers the phosphoryl group to the PTS EIIB type-3 domain. This gene was sequenced from pMG820, a laboratory-derived deletion of the naturally occurring plasmid pLP712.