A PALINDROMIC STRUCTURE IN THE PERICENTROMERIC REGION OF VARIOUS HUMAN-CHROMOSOMES

The primate-specific multisequence family chAB4 is represented with si milar to 40 copies within the haploid human genome. Former analyis rev ealed that unusually long repetition units (>35 kb) are distributed to at least eight different chromosomal loci. Remarkably varying copy-nu mbers within the genomes of closely related primate species as well as the existence of human specific subfamilies, which most probably aros e by frequent sequence exchanges, demonstrate that chAB4 is an unstabl e genomic element, at least in an evolutionary sense. To analyze the c hAB4 basic unit in more detail we established a cosmid contig and foun d it to be organized as inverted duplications of similar to 90 kb flan king a noninverted core sequence of similar to 60 kb. FISH as well as the analysis of chromosome-specific hybrid cell lines revealed a chrom osomal localization of chAB4 on chromosomes 1, 3, 4, 9, Y, and the per icentromeric region of all acrocentrics. Furthermore, we can detect ch AB4 sequences together with a satellites, beta satellites, and satelli te III sequences within a single chromosome 22-specific YAC clone, ind icating that chAB4 is located in close proximity to the centromere, at least on the acrocentrics, Hence, chAB4 represents an unstable genomi c structure that is located just in the chromosomal region that is ver y often involved in translocation processes.