MAPPING OF GENOMIC DNA LOOP ORGANIZATION IN A 500-KILOBASE REGION OF THE DROSOPHILA X-CHROMOSOME BY THE TOPOISOMERASE II-MEDIATED DNA LOOP EXCISION PROTOCOL

The recently developed procedure of chromosomal DNA loop excision by t opoisomerase II-mediated DNA cleavage at matrix attachment sites (S. V . Razin, R. Hancock, O. Iarovaia, O. Westergaard, I. Gromova, and G. P . Georgiev, Cold Spring Harbor Symp. Quant, Biol, 58:25-35, 1993; I. I . Gromova, B. Thompsen, and S. V. Razin, Proc. Natl. Acad. Sci. USA 92 :102-106, 1995) has been employed for mapping the DNA loop anchorage s ites in a 500-kb region of the Drosophila melanogaster X chromosome, E leven anchorage sites delimiting 10 DNA loops ranging in size from 20 to 90 kb were found within this region, Ten of these 11 anchorage site s colocalize with previously mapped scaffold attachment regions. Howev er, a number of other scaffold attachment regions are found to he loca ted in loop DNA.