The DNA-protein cross: a method for detecting specific DNA-protein complexes in crude mixtures

A method using crude cellular mixtures is described which permits identification of polypeptides and DNA fragments forming specific complexes. Our procedure incorporates elements of both 'Southern' and 'protein' blotting and combines, in two dimensions, the resolving power of a denaturing protein gel with that of an agarose DNA gel. Conditions for 'crossing' have been established using the lambda repressor-operator system: the specific complex can be detected by crossing total protein from bacteria overproducing the repressor with a mixture of total genomic fragments from a lysogen.