PROBABILITY-DISTRIBUTIONS OF SEQUENCES IN NONSPECIFIC DNA-LIGAND COMPLEXES

In this paper the probability-distribution function of different microstates as a consequence on the nonspecific interaction of a ligand with DNA is theoretically studied. Using the Sequence Generating Function (SGF) method, we have found equations for, the probability-distribution function of sizes of DNA-ligand bound sequences, as well for the probability distribution function of monomers in sequences of different sizes. These equations can be numerically solved, and yield valuable information on microscopic aspects of the system: size of the aggregates of bound ligand, fraction of base pairs in any of this aggregates, etc., corresponding to a macroscopically observed saturation function. The results are illustrated with three examples of nonspecific ligands (i.e. daunomycin, bovine pancreatic ribonuclease and protein GP32 of phage T4), whose interaction with DNA have been previously studied in our laboratory from both a theoretical and experimental point of view.