BIOCHEMICAL COMPONENTS OF A TRANSPORT SYSTEM

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The methylgalactoside permease (MeGalP) is a multicomponent transport system of Escherichia coli K-12 which mediates the intracellular accumulation of D-galactose and closely related sugars. The system requires three genes, mglA, mglB and mglC, for transport. The mglB gene codes for a periplasmic galactose-binding protein which is necessary for high affinity transport. The three genes controlling MegalP have been recently cloned and physically mapped on a 4.6-kb DNA fragment. Using gene amplification techniques, the products of mglA and mglC have been identified as membrane proteins of 52,000 (52K) and 38,000 (38K) daltons apparent molecular weight, respectively. The 52K protein has been isolated, purified, and used to elicit specific antibodies in mice and rabbits. We propose large scale preparation of purified 38K and 52K proteins for subsequent study of their properties. In addition, we plan experiments designed to establish functional relationships between the membrane proteins and the galactose-binding protein. mglB. To facilitate these experiements, we plan to develop a radioimmunoassay for the 52K protein. Another aim is to sequence the entire mgl operon DNA. The long-term objective is to fully understand the molecular mechanisms underlying sugar transport across cell membranes. This aim is directly related to health problems since practically all cells depend on sugar uptake for metabolic energy and structural maintenance.