[Structure of interphase chromatin of diploid and trisomal human cells studied by the technic of thermal denaturation in media of low ionic strength].

Fluorescent microscopy with the use of acridine orange has shown on a short-term human cell culture that the melting profiles of intact lymphocytes from normal subjects present the curves with maxima (F530) within a definite temperature range: 45, 65, 78, 85, 88 and 92 degrees C (+/- degrees C). The melting profiles of lymphocytes from patients with the Down syndrome present the curves with maxima at 65, 85, 88 and 92 degrees C. The melting of human cells in low ionic strength media as compared with physiological one causes the disappearance of the maxima on the chromatin melting curve and disappearance of the difference in the melting profiles of cell chromatin from normal subjects and patients. The data obtained allowed the conclusion that the use of acridine orange reveals the specificity of supermolecular organization of cell DNA complexes which is retained only under the conditions of physiological ionic strength medium. The organization of chromatin structure in patients with the Down syndrome was found to be changed as compared with controls.