DNA sequence analysis of a 1878-bp DNA fragment located downstream from the Rhizobium etli ptsN gene revealed the presence of an open reading frame coding for a protein of 300 amino acids. This protein is homologous to members of the PfkB subfamily of carbohydrate and carbohydrate phosphate kinases. Since the highest homology is observed with the ribokinases of Escherichia coli, Haemophilus influenzae and Bacillus subtilis, the isolated gene was named the R. etli rbsK gene. The eubacterial ribokinases form a cluster distinct from the cluster of ribokinase proteins of the archaebacteria Methanobacterium thermoautotrophicum, Methanococcus jannaschii and Sulfolobus solfoataricus, which form a more divergent group of proteins. R. etli RbsK has a molecular mass of 30.6 kDa and a calculated isoelectric point of 4.5. No homologues of Escherichia coli ORF284 and ORF90 were found downstream from R. etli ptsN.