Gene localization, size, and physical map of the chromosome of Streptococcus pneumoniae

A physical map of the Streptococcus (Diplococcus) pneumoniae chromosome, which is circular and 2,270 kbp in circumference, has been constructed. The restriction enzymes ApaI, SmaI, and SacII were used to digest intact chromosomes, and the fragments were resolved by field inversion gel electrophoresis (FIGE). The digests produced 22, 20, and 29 fragments, respectively. The order of the fragments was deduced from Southern blot hybridization of isolated labeled fragments to separated fragments of the various restriction digests. Genetic markers were correlated with the physical map by transformation of recipient cells with FIGE-isolated DNA fragments derived from genetically marked S. pneumoniae strains. In addition, markers were mapped by the hybridization of cloned genes to FIGE-separated restriction fragments. Six rRNA gene (rrn) clusters were mapped by hybridization to rrn-containing fragments of Haemophilus influenzae.