Kinetic persistence of cruciform structures in reconstituted minichromosomes

Cruciforms persist in reconstituted minichromosomes, as revealed by cleavage with specific nucleases and hybridization with synthetic oligonucleotides. Relaxation by topoisomerase I suggests that cruciforms are located mainly on internucleosomal DNA and that their persistence on minichromosomes may be due to kinetic effects. The analysis of the kinetic behaviour of cruciforms in minichromosomes shows a definite velocity of reabsorption with respect to stable cruciforms in supercoiled naked DNA. An explanation based on suppression of the untwisting of linker DNA due to adjacent nucleosomes is proposed.