The separation of DNA segments attached to proteins.

A simple assay for DNA segments bearing tightly bound proteins is described. This assay depends on the observation that proteins, of any type tested, bind quantitatively to glass fiber filters. When a protein is firmly attached to DNA, this DNA segment is retained while DNA not associated with protein will pass through the filter. Depending on the preparation of DNA, backgrounds as low as 3 × 10^?4 of the input DNA have been obtained. Using this technique it should be possible to specifically recover 1 restriction segment in 3000 that happens to be firmly bound to a protein. The protein or DNA-protein complex can be released by very dilute sodium dodecyl sulfate and after its removal by dialysis, nearly complete rebinding can be achieved. The procedure should find some use in removing traces of protein from DNA solutions as well as for the determination of proteins themselves. Single chain DNA and RNA are not retained but backgrounds are higher, ca. 2 × 10^?2. The procedure should have some application to single chain DNA and RNA-protein complexes.