Organization of a repetitive human 1.8 kb KpnI sequence localized in the heterochromatin of chromosome 15

We have isolated a repetitive 1.8 kb Kpnl DNA sequence which is amplified in the homogeneously staining regions of a human melanoma cell line. Under low stringency conditions this sequence (D15Z1) hybridized in situ to the centromeric heterochromatin of chromosomes 1, 9, 15p, 16, and distal Yq as well as to the the short arms of the other acrocentric chromosomes. Under conditions of high stringency, labelling was predominantly on the short arm of chromosome 15. D15Z1 was shown to be present at approximately 3,000 copies per haploid genome and organized in long tandem arrays showing restriction site heterogeneity. Sequences homologous to D15Z1 were highly enriched in the less dense shoulder region of a Ag⁺—Cs₂SO₄ gradient. Analysis of D15Z1 indicated that this sequence is composed of tandemly arranged imperfect repeats of the consensus 5 AATGG 3 similar to previously identified satellite III sequences. Digestion of D15Z1 with HinfI resulted in a series of restriction fragments making up a subset of the HinfI ladder components of satellites III and IV. These data suggest that D15Z1 represents a chromosome 15 specific domain of human satellites III or IV and that it makes up the major fraction of the heterochromatin of this chromosome. Possible relationships between this sequence and the cytochemical staining properties of human chromosomes with distamycin A/DAPI, D280/170, and antiserum to 5-methylcytosine are discussed.