MOLECULAR ANALYSIS OF THE SCRA AND SCRB GENES FROM KLEBSIELLA-PNEUMONIAE AND PLASMID PUR400 WHICH ENCODE THE SUCROSE TRANSPORT PROTEIN ENZYME IISCR OF THE PHOSPHOTRANSFERASE SYSTEM AND A SUCROSE-6-PHOSPHATE INVERTASE

The Klebsiella pneumoniae genes scrA and scrB are indispensable for su crose (Scr) utilisation. Gene scrA codes for an Enzyme IIScr (IIScr) t ransport protein of the phosphoenolpyruvate-dependent carbohydrate: ph osphotransferase system (PTS), while scrB encodes a sucrose 6-phosphat e specific invertase. A 3.7 kb scrAB DNA fragment has been cloned from K. pneumoniae and expressed in Escherichia coli. Its nucleotide seque nce was determined and the coding regions for scrA (1371 bp) and scrB (1401 bp) were identified by genetic complementation, enzyme activity tests and radiolabelling of the gene products. In addition, the nucleo tide sequence of the scrB gene from the conjugative plasmid pUR400 iso lated from Salmonella typhimurium was also determined and errors in th e previously published sequence of the scrA gene of pUR400 were correc ted. Extensive similarity was found between the sequences of ScrA and other Enzymes II, as well as between the two invertases and other sucr ose hydrolysing enzymes. Based on the analysis of seven IIScr proteins , a hypothetical model of the secondary structure of IIScr is proposed .