Binding of exogenous DNA by human lymphocytes and by their isolated plasma membranes

The binding of labeled bacterial DNA to human tonsil lymphocytes and to plasma membranes isolated from these cells involved macromolecules mainly located at the cell surface, since plasma membrane preparations showed properties in common with those of viable cells. DNA binding to lymphocytes was a dissociable, saturable, time, temperature, pH and concentration dependent process. A double reciprocal plot of the data obtained from DNA saturation curves gave an apparent dissociation constant of about 4 X 10(-10) M. The process of interaction of 3H-DNA with lymphocyte membranes gave a complex Scatchard plot, whose first slope yielded an apparent dissociation constant similar to that obtained for DNA-cell interaction. Binding was shown to be specific for DNA because RNA did not displace the bound DNA. Double stranded DNA was preferentially bound relative to single stranded DNA. Temperatures greater than 55 degrees C abolished the binding capacity. Results of experiments in which pH and salt concentration were varied point to the importance of conformational changes of the nucleic acid in the binding process.