Fluorescence of complexes of acridine dye with synthetic polydeoxyribonucleotides: A physical model of frameshift mutation

Fluorescence measurements (quantum yield, polarization and lifetime) were made on complexes of a series of acridine dyes with two polydeoxyribonucleotides (poly[d(A-T)] and poly(dG)·poly(dC)) at a high nucleotide/dye ratio (>100). The main results are as follows. 1. (a) The quantum yield is increased in the case of complexes with poly[d(A-T)] but an almost complete quenching of fluorescence is observed with poly(dG)·poly(dC), except in the case of acridine orange. 2. (b) Bound acridine orange has a polarization value of 0.31 with poly[d(A-T)], 0.36 with poly(dG)·poly(dC), and an intermediate value with DNA. 3. (c) If ethidium bromide is compared to acridine dyes, one finds a 50-fold increase of quantum yield with poly[d(A-T)]but a value close to zero with poly(dG)·poly(dC). The correlation between the mutagenic properties of a given acridine dye and its quenching of fluorescence when intercalated close to a G.C pair leads us to assume that mutation depends on the electronic state of G (or G.C pair). If examples of frameshift mutations are examined from this new point of view, in every case the mutational event could be explained with very simple rules, according to the position of the modified G in one strand or the other. These rules have of course to be tested by a greater number of genetic experiments but they provide at least a new, interesting working hypothesis.