Clones from an 840-kb fragment containing the 5' region of the DMD locus enriched by pulsed field gel electrophoresis

Detailed analysis of a large region of genomic DNA is facilitated by generating overlapping clones covering the entire region. These clones are usually obtained by bidirectional "walking" using either bacteriophage lambda or cosmid cloning vectors. This is a slow procedure when starting from a single start site. Multiple start sites are an advantage, and here we describe a method of generating clones from an extensive region of the Duchenne muscular dystrophy locus by preparative pulsed field gel electrophoresis using the chromosome of interest isolated in a cell hybrid. We have generated 12 clones mapping to an 840-kb SfiI fragment of DNA from the Xp2.1 region of the X chromosome, where the DMD gene has been localized. Further localization of these clones to the four subregions of the 840-kb fragment indicates that the clones are distributed throughout the fragment. The feasibility of using this approach to generate probes close to other loci is discussed.