Physical map location of the Escherichia coli gene encoding phosphoglycerol transferase I.

Membrane-derived oligosaccharides (MDO) are found as soluble components of the periplasmic compartment of Escherichia coli (15). They are a family of closely related oligosaccharides containing 6 to 10 glucose units joined by 3-1,2 and 3-1,6 linkages and are variously substituted with succinic acid 0 ester, phosphoethanolamine, and sn-1-phosphoglycerol (7, 14). The mdoB locus (4, 5) encodes phosphoglycerol transferase I, an enzyme which catalyzes the in vitro transfer of phosphoglycerol residues from phosphatidylglycerol to MDO or to the artificial substrate arbutin (p-hydroxyphenyl-o-D-glucoside) (6). Because this enzyme has its active site on the periplasmic side of the cytoplasmic membrane, it also catalyzes the in vivo transfer of phosphoglycerol to arbutin added to the medium (2), although arbutin cannot enter the cytoplasm. Mutants defective at the mdoB locus cannot transfer phosphoglycerol residues to arbutin in vivo and synthesize MDO devoid of phosphoglycerol residues (5). One