The nucleotide sequence of the ugp genes of Escherichia coli K-12, which encode a phosphate-limitation inducible uptake system for sn-glycerol-3-phosphate and glycerophosphoryl diesters, was determined. The genetic organization of the operon differed from previously published results. A single promoter, containing a putative pho box, was detected by S1-nuclease mapping. The promoter is followed by four open reading frames, designated ugpB, A, E and C, which encode a periplasmic binding protein, two hydrophobic membrane proteins and a protein that is likely to couple energy to the transport system, respectively. The sequences of the proteins contain the characteristics of several other binding protein-dependent transport systems, but they seem to be particularly closely related to the maltose system.