Abstract
Sequences that did or did not reassociate at 75 dagrees C (stable and unstable, respectively) were isolated from total repetitive Xenopus laevis DNA. Sequence complexities or frequencies were determined by self (minicot) or DNA excess (slave minicot) reassociations at 60 degrees C. Stable sequences were five times shorter and four times more frequent than unstable sequences. Reassociations at 75 degrees C or at 50 degrees C were used to establish apparent sequence frequencies at these criteria. Interspersion curves at either 60 degrees C or 75 degrees C and low Cot reassociation of long fragments of total X. laevis DNA at either 60 degrees C or 75 degrees C, followed by S1 digestion and agarose chromatography, were used to determine genome arrangement of the stable and unstable classes of sequence. Reassociation at high temperature was found to permit the fractionation of repetitive sequences into two populations of differing characteristics.