Altered lipopolysaccharide characteristic of the I69 phenotype in Haemophilus influenzae results from mutations in a novel gene, isn.

The 169 phenotype of Haemophilus influenzae results from a mutation leading to a lipopolysaccharide molecule consisting only of lipid A and a single phosphorylated 2-keto-3-deoxyoctulosonic acid residue. In this paper we describe the identification of a gene which, when mutated, results in the 169 phenotype. We have named the gene isn. The predicted amino acid sequence of Isn is homologous to the product of the lmbN gene involved in the biosynthesis of the sugar-containing antibiotic lincomycin by Streptomyces lincolnensis. lsn is situated between two loci that are homologous to the dpp and art periplasmic permease systems in Escherichia coli. Northern (RNA) blot and primer extension analyses reveal that isn is transcribed as a monocistronic mRNA. Potential functions of Isn protein are discussed.