THE 724 FAMILY OF DNA-SEQUENCES IS INTERSPERSED ABOUT THE PERICENTROMERIC REGIONS OF HUMAN ACROCENTRIC CHROMOSOMES

We descirbe the organization of the complex, interspersed 724 family of DNA sequences that is distributed in multiple copies about the pericentromeric region of human acrocentric chromosomes. 724 family members were isolated using an efficient recombination-based assay for nucleotide sequence homology to screen a human genomic library. Eight related but distinct 724 family members were isolated that hybridized to a total of 20 different human-genomic EcoRI DNA fragments spanning 100,000 base pairs. In contrast with tandemly clustered satellite and ribosomal DNA sequencies also located on the short arms of human acrocentric chromosomes, 724 family members are interspersed. No evidence for local interspersion or homologyy between 724 family members and ribosomal or satellite DNA sequencies was found. Juxtaposition of the complex 724 family to the nucleolus organizer region was a recent event in primate evolution. The unique organization of 724 family members on each of the five human acrocentric chromosomes indicates that the 724 family continues to evolve within the human karyotype.