Molecular structure and evolution of DNA sequences located at the alpha satellite boundary of chromosome 20

We have isolated and characterised one PAC clone (dJ233C1) containing a lin kage between alphoid and non-alphoid DNA. The non-alphoid DNA was found to map at the pericentromeric region of chromosome 20, both on p and q sides, and to contain homologies with one contig (ctg176, Sanger Centre), also loc ated in the same chromosome region. At variance with the chromosome specifi city shown by the majority of non-alphoid DNA, a subset of alphoid repeats derived from the PAC yielded FISH hybridisation signals located at the cent romeric region of several human chromosomes, belonging to three different s uprachromosomal families. The evolutionary conservation of this boundary re gion was investigated by comparative FISH experiments on chromosomes from g reat apes. The non-alphoid DNA was found to have undergone events of expans ion and transposition to different pericentromeric regions of great apes ch romosomes. Alphoid sequences revealed a very wide distribution of FISH sign als in the great apes. The pattern was substantially discordant with the da ta available in the literature, which is essentially derived from the centr al alphoid subset. These results add further support to the emerging opinio n that the pericentromeric regions are high plastics, and that the alpha sa tellite junctions do not share the evolutionary history with the main subse ts. (C) 2000 Elsevier Science B.V. All rights reserved.