DIFFERENTIAL DIGESTION OF THE CENTROMERIC HETEROCHROMATIC REGIONS OF THE 5-AZACYTIDINE-DECONDENSED HUMAN-CHROMOSOME-1, HUMAN-CHROMOSOME-9, HUMAN-CHROMOSOME-15, AND HUMAN-CHROMOSOME-16 BY NDEII AND SAU3AI RESTRICTION ENDONUCLEASES

A study on the factors involved in chromosome digestion by restriction endonuclease was carried out on 5-azacytidine treated and untreated h uman chromosomes 1, 9, 15 and 16 by using NdeII and Sau3AI isoschizome rs. After treatment with 5-azacytidine, chromosomes 1, 9, 15, and 16 s howed two differentiated areas at the centromeric regions: the centrom ere, fully condensed, and the pericentromeric heterochromatin, deconde nsed. Chromosomes not treated with 5-azacytidine after digestion with Sau3AI and NdeII showed all the centromeric regions undigested, except pair number 1, digested at the pericentromeric area. Digestion of the 5-azacytidine decondensed chromosomes with Sau3AI and NdeII showed th e centromeres undigested in the four chromosome pairs while the perice ntromeric heterochromatin appeared largely digested. Other factors, di fferent to target distribution, are necessary to explain the pattern o f restriction endonuclease digestion observed in this communication.