CONCERTED EVOLUTION OF PRIMATE ALPHA-SATELLITE DNA - EVIDENCE FOR AN ANCESTRAL SEQUENCE SHARED BY GORILLA AND HUMAN X-CHROMOSOME ALPHA-SATELLITE

To understand evolutionary events in the formation of higher-order repeat units in alpha satellite DNA, we have examined gorilla sequences homologous to human X chromosome alpha satellite. In humans, alpha satellite on the X chromosome is organized as a tandemly repeated, 2.0 × 103 base-pairs (bp) higher-order repeat unit, operationally defined by the restriction enzyme BamHI. Each higher-order repeat unit is composed of 12 tandem approximately 171 base-pair monomer units that have been classified into five distinct sequence homology groups. BamHI-digested gorilla genomic DNA hybridized with the cloned human 2 × 103 bp X alpha satellite repeat reveals three bands of sizes approximately 3.2 × 103, 2.7 × 103 and 2 × 103 bp. Multiple copies of all three repeat lengths have been isolated and mapped to the centromeric region of the gorilla X chromosome by fluorescence in situ hybridization. Long-range restriction mapping using pulsed-field gel electrophoresis shows that the 2.7 × 103 and 3.2 × 103 bp repeat arrays exist as separate but likely neighboring arrays on the gorilla X, each ranging in size from approximately 200 × 103 to 500 × 103 bp, considerably smaller than the approximately 2000 × 103 to 4000 × 103 bp array found on human X chromosomes. Nucleotide sequence analysis has revealed that monomers within all three gorilla repeat units can be classified into the same five sequence homology groups as monomers located within the higher-order repeat unit on the human X chromosome, suggesting that the formation of the five distinct monomer types predates the divergence of the lineages of contemporary humans and gorillas. The order of 12 monomers within the 2 × 103 and 2.7 × 103 bp repeat units from the gorilla X chromosome is identical with that of the 2 × 103 bp repeat unit from the human X chromosome, suggesting an ancestral linear arrangement and supporting hypotheses about events largely restricted to single chromosome types in the formation of alpha satellite higher-order repeat units. © 1990.