Fiber-FISH: experiences and a refined protocol.

One of the most time-consuming steps in positional cloning is the physical mapping of probes from the critical chromosomal region and the assembly of a genomic contig of large insert probes. New high-resolution Fiber-FISH techniques have significantly facilitated this tedious task by enabling rapid direct visualization of the order, degree of overlap and gap sizes of adjacent large insert clones. We have developed a method, where agarose-embedded DNA (PFGE block) is used as a source for preparing linearized DNA targets on microscope slides. This modification of the fiber-FISH technique has been successfully used in physical mapping in the 1-300 kb range as well as for detecting genomic rearrangements. Here, we present a refined protocol of our original technique. The application of this technique to agarose embedded yeast cells is also demonstrated. Finally, critical steps and trouble shooting of the method are addressed.