High resolution mapping using fluorescence in situ hybridization to extended DNA fibers prepared from agarose-embedded cells.

Fluorescence in situ hybridization (FISH) and pulse field gel electrophoresis (PFGE) are essential techniques in physical mapping and in positional cloning. We present a technique that utilizes agarose-embedded high molecular weight DNA prepared for PFGE as a target for FISH. The agarose blocks are melted, and the DNA is extended on a poly-L-lysine-coated microscope slide. The resulting DNA fibers appear on the slide as long straight strands and are a suitable target for high resolution FISH mapping as demonstrated here with cosmid and plasmid hybridizations.