Abstract
We have devised a method for mapping sites on DNA within the nucleus that are protected against nuclease attack by interaction with bound protein or other factors. This "footprinting" method uses an end-labeled sequence-specific DNA probe, which is annealed to the DNA from nuclear digests under carefully controlled conditions. The annealed complexes are treated with single-strand-specific nuclease, the resulting duplex molecules are electrophoresed on gels, and the gels are autoradiographed. The high sensitivity and resolution of the method have made it possible to obtain a detailed map of DNase I cutting patterns in the 5' flanking sequence of the chicken adult beta (beta A)-globin gene within nuclei from various tissues. In nuclei from adult erythrocytes, this domain is hypersensitive to nucleases. However, we detect within the domain two well-defined regions that are protected against attack, indicating the presence of one or more bound factors. Nuclei from oviduct or 5-day-old embryonic erythrocytes, in which the domain is not hypersensitive, show limited and different patterns of protection.