The equation describing small molecule binding to the n lattice residues and covering n+1 consecutive lattice residues (n≥2) has been derived by using simple conditional probabilities, and has been applied to the systems of the interaction of trans-[Pt(NH~3)~2Cl~2] with polynucleotides. The binding constants and the binding site size of trans-Pt to polyG, polyA and polyC at pH=5 and 7, and the ratio of overlap-cross linking to nonoverlap-cross linking formed between trans-Pt and polyN have been obtained.

Key words: POLYNUCLEOTIDE, PLATINUM COMPLEX, MODELS, RESIDUE (BIOCHEMISTRY), MULCH