The ugp structural genes, coding for the pho regulon dependent sn-glycerol-3-phosphate transport system, were cloned in pBR322 and characterized. The expression of the cloned ugp system was phoB dependent. Cells containing the ugp plasmid overproduced the G3P binding protein upon phosphate starvation. Tn 5 mutagenesis of the cloned DNA revealed that the ugp genes are organized in two separate operons which comprise at least four genes: ugpB and ugpD constitute one operon, ugpA and ugpC constitute the other. The structural gene for the G3P binding protein (G3PBP) is ugpB. The ugpC gene product was also synthesized in minicells as a polypeptide, with an apparent molecular weight of 40,000. No gene products could be assigned to the ugpA and ugpD genes. Hybridization experiments allowed the physical characterization of 20 kb of DNA adjacent to the ugp genes on the E. coli chromosome including the liv genes.
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