PHYSICAL MAPPING ACROSS THE DIHYDROFOLATE REDUCTASE-THYMIDYLATE SYNTHASE CHROMOSOME OF LEISHMANIA-MAJOR

We have used a chromosome-specific approach to generate a 300 kb long 'contig' across Leishmania major 500 kb chromosome. Clones from a 13-h it genomic library served as templates to generate end-specific probes that were used in hybridization to a high density array of the librar y. The 'contig' generated contained 12 markers uniformly spaced. Three restriction endonucleases were mapped within the map extending its re solution. Map extension indicated a peculiar feature of sequence organ ization in subtelomeric regions where chromosome-specificity of mappin g is lost. End-probes generated from clones mapping to the extremes of a 300 kb 'contig' rescued a high percentage of 2 types of clones from the genomic library, 1 of which showed positive hybridization to the hexameric telomere repeat. Fine mapping at these regions revealed that these 2 clones contained elements common to all chromosomes of the pa rasite. The physical map generated constitutes ready-to-use data for t he study of many aspects of genome organization. Being cloned in a shu ttle vector, the genomic sequences reordered in the map can be used to generate genetic information by transfection into the parasite.