BANDING HUMAN-CHROMOSOMES USING A COMBINED C-BANDING-FLUOROCHROME STAINING TECHNIQUE

Slides pretreated for C-banding and stained with DAPI or CMA3 show dif ferent banding patterns in human metaphase chromosomes compared to tho se obtained with either standard Giemsa C-banding or fluorochrome stai ning alone. Human chromosomes show C-plus DA-DAPI banding after C-band ing plus DAPI and enhanced R-banding after C-banding plus Chromomycin A3 staining. If C-banding preferentially removes certain classes of DN A and proteins from different chromosome domains, C-banding pretreatme nt may cause a differential DNA extraction from G- and R-bands in huma n chromosomes, resulting in a preferential extraction of DNA included in G-bands. This hypothesis is partially supported by the selective cl eavage and removal of DNA from R-bands of restriction endonuclease Hae III with C-banding combined with DAPI or Chromomycin A3 staining. Stru ctural factors relating to regional differences in DNA and/or proteins could also explain these results.