CHROMOSOME-SPECIFIC ALPHA-SATELLITE DNA FROM THE CENTROMERE OF CHIMPANZEE CHROMOSOME-4

The centromeric regions of human and primate chromosomes are character ized by diverged subsets of tandemly repeated alpha-satellite DNA. Com parison of the alpha-satellites on known homologous chromosomes in hum an and chimpanzee provides insight into the very rapid evolution of sa tellite DNA sequences and the mechanisms that shape complex genomes. B y using oligonucleotide primers specific for a conserved region of hum an alpha-satellite DNA, we have amplified a chromosome-specific alpha- satellite subset from the chimpanzee genome by the polymerase chain re action. Fluorescence in situ hybridization showed that clones p alpha PTR4N and p alpha PTR4H are homologous to sequences at the centromere of the chimpanzee chromosome 4. This alpha-satellite subset is organiz ed as a series of pentameric (higher-order) repeats, operationally def ined by digestion of genomic DNA with HaeIII, MboI, RsaI, SstI, and Xb aI. The lengths of four independent centromeric arrays measured by pul sed-field gel electrophoresis varied between 800 and 3,500 kb (mean = 1,850 kb, SD = 1,000 kb). Nucleotide sequence analysis demonstrated th at chimpanzee chromosome 4 alpha-satellite is most closely related to the suprachromosomal subfamily II, which is evolutionarily different f rom the subfamily I to which the alpha-satellite on the homologous hum an chromosome 5 belongs. This implies that the human-chimpanzee sequen ce divergence has not arisen from a common ancestral alpha-satellite r epeat(s) but instead represents concerted evolution of distinct repeat s on homologous chromosomes.