COUNTERSTAINED ENHANCEMENT OF TAQI RESISTANT SITES AFTER DISTAMYCIN ADIAMIDINOPHENYLINDOLE TREATMENT

Numerous selective and differential staining techniques have been used to investigate the hierarchical organisation of the human genome. Thi s investigation demonstrates the unique characteristics that are produ ced on fixed human chromosomes when sequential procedures involving re striction endonuclease TaqI, distamycin A (DA) and 4',6-diamidino-2-ph enylindole (DAPI) are employed. TaqI produces extensive gaps in the he terochromatic regions associated with satellite II and III DNAs of hum an chromosomes 1, 9, 15, 16 and Y. DA/DAPI selectively highlights, as brightly fluorescent C-bands, the heterochromatin associated with the alpha, beta, satellite II and III DNAs of these chromosomes. When DA a nd DAPI are used on chromosomes before TaqI digestion, and then staine d with Giemsa, the centromeric regions appear to be more resistant, pr oducing a distinct C-banding pattern and gaps in the heterochromatin r egions. Sequential use of the DA/DAPI technique after TaqI treatment p roduces a bright fluorescence on the remaining pericentromeric regions of chromosomes 1, 9, 16 and Y, which also displayed a cytochemically unique banding pattern. This approach has produced specific enhanced c hromosomal bands, which may serve as tools to characterize genomic het erochromatin at a fundamental level.