Molecular structure and evolution of an alpha satellite/non-alpha satellite junction at 16p11.

We have determined the detailed molecular structure and evolution of an alpha satellite junction from human chromosome 16p11. The analysis reveals that the alpha satellite sequence bordering the transition lacks higher-order structure and that the non-alpha satellite portion consists of a mosaic of duplicated segments of complex evolutionary origin. The 16p11 junction was formed recently (5-10 million years ago) by the duplication and transposition of genomic segments from Xq28 and 4q24. Once this mosaic structure was formed, a larger complex was spread among multiple pericentromeric regions. This resulted in the formation of large (>62 kb) paralogous segments that share a high degree ( approximately 97%) of sequence similarity. Both phylogenetic and comparative analyses indicate that these pericentromeric-directed duplications occurred around the time of the divergence of the human, gorilla and chimpanzee lineages, resulting in the subtle restructuring of the primate genome among these species. The available data suggest that such chimeric structures are a general property of several different human chromosomes near their alpha satellite junctions.