Why Centric Regions of Quinacrine-treated Mouse Chromosomes show Diminished Fluorescence

Abstract

Rowley and Bodmer¹ reported that the centric regions of quinacrine-treated mouse chromosome preparations show less fluorescence intensity than the remainder of the chromosome. They argued that because these centric regions contain a type of DNA that is richer in AT base pairs than unique sequence DNA, they would be expected to show diminished fluorescence according to the model proposed by Caspersson et al.², according to which localised quinacrine fluorescence was attributed to the preferential binding of quinacrine mustard to the N-7 position of guanylyl residues in DNA. Thus, one would expect a relative paucity of guanylyl residues in the DNA of the centric regions to be associated with diminished fluorescence. It has since been shown^3,4 that enhanced quinacrine fluorescence is due to AT base pairs, and studies of a series of GC-containing DNA polymers indicated that GC base pairs (or G alone) actually quenched fluorescence⁴. These observations did not explain why the centric regions of mouse chromosomes with their relatively greater abundance of AT base repairs show diminished quinacrine fluorescence.