CHARACTERIZATION OF THE DTDP-RHAMNOSE BIOSYNTHETIC GENES ENCODED IN THE RFB LOCUS OF SHIGELLA-FLEXNERI

The nucleotide sequence of the proximal half of the rfb region of Shig ella flexneri has been determined, and the genes encoding enzymes invo lved in the biosynthesis of dTDP-rhamnose have been identified. These genes show strong homology to the rfb genes encoding dTDP-rhamnose bio synthesis in Salmonella enterica serovar typhimurium (strain LT2) and S. enterica serovar anatum (strain M32) (Jiang et al, 1991; Wang et al , 1992). An open reading frame upstream of rfbB was also identified wh ich encoded a protein having strong similarity with GalU, and has been designated galF. GalF has 92% amino acid sequence identity with an S. enterica LT2 gene, orf2X8, which is similarly situated upstream of rf bB (Jiang ef ah, 1991). The T7 expression system was utilized to ident ify proteins corresponding to those predicted from DNA sequence analys is. The similarity of the predicted proteins with proteins that are fu nctionally identical or related, and with others of unknown function f rom the Yersinia enterocolitica O3 rfb region, and in the Escherichia coil K-12 rff region are also described. We have re-addressed the assi gnment of each gene of the dTDP-rhamnose pathway with the known enzyme s of the pathway, in particular rfbC and rfbD. A reporter plasmid to d etect genes encoding enzymes of the dTDP-rhamnose pathway is described . An analysis of the intergenic region between galF and rfbB has been made, and comparison with the same region from S. enterica LT2 discuss ed.