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