Peculiarities of the reassociation kinetics of fast repeating sequences of thermolabile fractions of hepatoma Zaidel DNA

: The six fractions of rat liver DNA (DNAL) and hepatoma Zaidel DNA (DNAHZ) were obtained by thermal fractionation of these DNAs on a HAP column at equivalent temperature intervals. The percent of two thermolabile fractions obtained at 62--78 degrees is approximately 10% higher for DNAHZ than for DNAL. The reassociation kinetics were carried out till Cot = 5.10(-1). Computer analysis of the kinetics showed considerable difference between the parameters (percent of the sequence and rate constant) only for these thermolabile fractions DNAL and DNAHZ. The two-fold reduction of the reassociation rate for the second thermolabile fraction DNAHZ (63--78 degrees) can be associated with the presence of short uncomplementary pieces in the fast repeating sequences. On the other hand the increase of the rate constant for the initial part of the kinetics reassociation of the first thermolabile fraction (62--73 degrees) of DNAHZ is due to the nicks which are revealed by alkali sucrose centrifugation of the DNAHZ fractions.