IN HUMAN-CHROMOSOMES TELOMERIC REGIONS ARE ENRICHED IN CPGS RELATIVE TO R-BANDS

Human chromosomes were in situ nick-translated using as nicking agents the endonucleases MspI (CCGG), its methyl-sensitive isoschizomer HpaII, HaeIII (GGCC), SacII (CCGCGG), EcoRI (GAATTC) and DNaseI. We show that in metaphase chromosomes R-bands are enriched, as compared with G-bands, in the dinucleotide CpG but no more than what is expected on the basis of their relative G+C content. The telomeric regions, on the contrary, besides having a chromatin conformation that is particularly relaxed and accessible to endonucleases, also show an enrichment in CpGs.