Selective digestion of human metaphase chromosomes by Alu I restriction endonuclease

Human cytological preparations have been digested with Alu I restriction endonuclease (Endo R Alu I) and subsequently stained with acridine orange. Metaphase chromosomes treated in this way revealed a clear-cut bright/ dull longitudinal differentiation. It has been postulated that these cytological findings could be related to the selective digestion, by Alu I, of all DNA with the exception of some heterochromatic, possibly satellite, fractions.