[The metaphase chromosome: functional inertia and ability related to the presence of sequences of single-stranded DNA].

Isolated metaphase chromosomes from KB cells were used as template in an in vitro DNA synthesis assay. In these conditions, no synthesis was noticed, confirming template inactivity of isolated metaphase chromosomes. DNA synthesis was noticed after a pretreatment with either methanol-acetic acid or RNase A. Analysis of in vitro synthesized polydeoxyribonucleotides showed two fractions of 4 S and 7-8 S. These results suggest the presence in metaphase chromosome of single stranded DNA sequences. Such sequences are shown in DNA extracted from chromosomes. They would preexist in this organelle and would be unmasked by the treatments that restore template activity of metaphase chromosome.