Chromosome regions containing DNAs of known base composition,specifically evidenced by 2,7-di-t-butyl proflavine

After staining by a new proflavine derivative (2,7-di-t-butyl proflavine, DBP), which specifically binds to the A-T base pairs of DNA by an external process, the constrictions of the human chromosomes 1, 16 and to a lesser extent 9 and the centromeric regions of the chromosomes (except the Y) of Mus musculus are brightly fluorescent. These chromosome regions are known to contain repetitive DNAs rich in A-T. On the contrary, the centromeric regions of the autosomes of Bos taurus, which contain a G-C rich DNA, are faintly fluorescent. The arms of the chromosomes of the three species display a banding similar to, but fainter than, the Q-banding. These results are discussed in correlation with physico-chemical studies on the binding and fluorescence processes of the dye bound to DNA and to nucleohistone. The staining properties of DBP are compared to those of quinacrine, quinacrine mustard and proflavine, three intercalative dyes which are also supposed to reveal the A-T base pairs along the chromosomes, but are faintly fluorescent on the human and murine A-T rich regions. This comparison leads us to discuss the mechanisms responsible for the chromosomal banding in relation to DNA base composition and repetitiveness, protein distribution and packing of the chromatin fibers, along the chromosomes.