THE PHYSICAL MAP OF THE CHROMOSOME OF A SEROGROUP-A STRAIN OF NEISSERIA-MENINGITIDIS SHOWS COMPLEX REARRANGEMENTS RELATIVE TO THE CHROMOSOMES OF THE 2 MAPPED STRAINS OF THE CLOSELY-RELATED SPECIES N-GONORRHEA

A physical map of the chromosome of N, meningitidis Z2491 (serogroup A , subgroup IV-l) has been constructed, Z2491 DNA was digested with Nhe I, SpeI, SgfI, PacI, BglII, or PmeI, resulting in a limited number of fragments that were resolved by contour-clamped homogeneous electric f ield (CHEF) electrophoresis. The estimated genome size for this strain was 2,226 kb. To construct the map, probes corresponding to single-co py genes or sequences were used on Southern blots of chromosomal DNA d igested with the different mapping enzymes and subjected to CHEF elect rophoresis. By determining which fragments from different digests hybr idized to each specific probe, it was possible to walk back and forth between digests to form a circular macrorestriction map. The intervals between mapped restriction sites range from 10 to 143 kb in size, A t otal of 117 markers have been placed on the map; 75 represent identifi ed genes, with the remaining markers defined by anonymous cloned fragm ents of neisserial DNA, Comparison of the arrangement of genetic loci in Z2491 with that in gonococcal strain FA1090, for which a physical m ap was previously constructed, revealed complex genomic rearrangements between the two strains, Although gene order is generally conserved o ver much of the chromosome, a region of approximately 500 kb shows tra nslocation and/or inversion of multiple blocks of markers between the two Strains, Even within the relatively conserved portions of the maps , several genetic markers are in different positions in Z2491 and FA10 90.