Loop-size spacings between CGCG clusters in long segments of human DNA

The CGCG tetranucleotides are clustered inside the CpG islands in the genomes of vertebrates. In order to study the distribution of the islands in the human chromosome we have mapped the loci sensitive to the CGCG specific restriction nuclease, in a 1.5 Mb long DNA segment cloned as Yeast Artificial Chromosome (YAC). The sites most sensitive to Bsh 1236 I nuclease show chromosomal loop-size spacing. This result, as well as the result of nucleotide sequence analysis of long genomic segments, suggests that the CGCG are organised in clusters (not always undermethylated) which are coincident with GC peaks on the sine wave-like curve representing DNA composition along the mammalian chromosome.