Northern blot mapping: a procedure for mapping mRNA immobilized on nitrocellulose by probing with end-labeled DNA fragments.

A simple method for mapping RNA on a Northern blot with a mixture of end-labeled DNA fragments is described. The DNA fragments are labeled either in 5' or in 3' directly after digestion by restriction enzyme(s) and used without any further purification step as probe to hybridize a Northern blot. After autoradiography, the DNA fragments hybridized to each mRNA species are recovered by heating the nitrocellulose and analyzed on denaturing polyacrylamide or agarose gels. This method indicates which DNA fragment hybridizes with which mRNA species and requires far fewer different manipulations than successive hybridization of a Northern blot with several nick-translated purified DNA fragments.