Plasmid-mediated sucrose metabolism in Escherichia coli K12: mapping of the scr genes of pUR400

Abstract

The scr genes located on plasmid pUR400 and responsible for sucrose (Scr) metabolism of Escherichia coli K12 and other enteric bacteria have been cloned on a 9.3 kb DNA fragment. The different genes were mapped by transposon insertion mutagenesis, by restriction endonuclease and deletion mapping, and the corresponding gene products were identified. Besides the known structural genes scrA, coding for an EnzymeII(Scr) (45 kD) of the phosphoenolypyruvate-dependent phosphotransferase system (PTS), and scrB, coding for a sucrose 6-phosphate hydrolase (invertase) (55 kD), two new structural genes were discovered. Gene scrK apparently codes for an intracellular and ATP-dependent fructokinase (39 kD), while scrY seems to code for a sucrose porin (58 kD) in the outer cell membrane. No genes for an Enzyme III(Scr) of the PTS or for (a) glycosyltransferase(s) were detected. The four genes form an scr operon (gene order, scrK scrY scrA scrB, transcription from K to B), regulated by a repressor (gene scrR, 37 kD) and inducible by sucrose, fructose and fructose-containing oligosaccharides.