CHARACTERIZATION OF THE CASSETTE CONTAINING GENES FOR TYPE-3 CAPSULARPOLYSACCHARIDE BIOSYNTHESIS IN STREPTOCOCCUS-PNEUMONIAE

The capsular polysaccharide is the major virulence factor of Streptoco ccus pneumoniae. Previously, we identified and cloned a region from th e S. pneumoniae chromosome specific for the production of type 3 capsu lar polysaccharide. Now, by sequencing the region and characterizing m utations genetically and in an in vitro capsule synthesis assay, we ha ve assigned putative functions to the products of the type-specific ge nes. Using DNA from the right end of the region in mapping studies, we have obtained further evidence indicating that the capsule genes of e ach serotype are contained in a gene cassette located adjacent to this region. We have cloned the region flanking the left end of the casset te from the type 3 chromosome and have found that it is repeated in th e S. pneumoniae chromosome. The DNA sequence and hybridization data su ggest a model for recombination of the capsule gene cassettes that not only describes the replacement of capsule genes, but also suggests an explanation for binary capsule type formation, and the creation of no vel capsule types.