STRUCTURAL AND FUNCTIONAL ORGANIZATION OF THE EXOPOLYSACCHARIDE BIOSYNTHESIS GENES IN RHIZOBIUM LEGUMINOSARUM BV. VICIAE VF39

The 7181-nt XhoI-MluI fragment of Rhizobium leguminosarum by. viciae VF39 chromosomal DNA was sequenced. Mutations in this region disturb the synthesis of an extracellular polysaccharide and nodulation in Vicia faba roots. Computer analysis revealed eight open reading frames designated pssE,D,C,F,G,H,I and orf8. All genes showed expression in a T7 promoter/RNA polymerase system. Comparison of the deduced amino acid sequences of their protein products with known protein sequences and analysis of exopolysaccharides in mutants showed that the pssE,D,C,EG,H,I genes code for glycosyltransferases consecutively involved in the synthesis of the octasaccharide unit of the polysaccharide.