REGION-2 OF THE ESCHERICHIA-COLI K5 CAPSULE GENE-CLUSTER ENCODING PROTEINS FOR THE BIOSYNTHESIS OF THE K5 POLYSACCHARIDE

The nucleotide sequence of region 2 of the Escherichia coli K5 capsule gene cluster has been determined. This region, essential for the bios ynthesis of the K5 polysaccharide, contained four genes, termed kfiA-D . The G+C ratio was 33.4%, which was lower than the typical G+C ratio for E. coli and that of the flanking regions 1 and 3 in the K5 capsule gene cluster. Three major RNA transcripts were detected within region 2 by Northern blotting and three promoters located by transcript mapp ing. Promoter activity was confirmed by promoter-probe analysis. The p redicted amino acid sequence of KfiC had homology to a number of glyco syl transferase enzymes and overexpression of the kfiC gene resulted i n increased K5 transferase activity. The predicted amino acid sequence of KfiD had homology to a number of NAD-dependent dehydrogenase enzym es and was demonstrated to be a UDP-glucose dehydrogenase that catalys es the formation of UDP-glucuronic acid from UDP-glucose.