A cross-hybridization method for DNA mapping with photobiotin-labeled probes.

An efficient procedure combining the Southern Cross method described by H. Potter and D. Dressler (1986, Gene 48, 229-239) and the use of nonradioactive reporter molecules which allows fast restriction mapping of DNA molecules up to 40 kb is described. In this method, photobiotin-labeled fragments for one restriction enzyme cross-hybridize with at least five unlabeled digests transferred onto nylon membranes. Hybridization spots are revealed on recipient membranes at a homologous fragment cross, allowing direct restriction map construction. In comparison with 32P "cross-blot" hybridization, photobiotin labeling is safer, faster, and easier to dispose of.