SITE-SPECIFIC RETROTRANSPOSITION OF L1 ELEMENTS WITHIN HUMAN ALPHOID SATELLITE SEQUENCES

In the course of a search for microsatellites as centromeric polymorph ic markers at the 3' ends of Alu or L1 elements, we observed a much hi gher frequency of L1 than Alu elements embedded within alpha satellite DNA. By sequence analysis of the L1 elements at their alphoid locus o f insertion, we found that the insertion site was specific, with the c onsensus being (Py)(2-10)/(Pu)(3-7). All potential sites within the co nsensus alphoid 171-bp repeat are occupied by such elements. This conf irms the finding by Feng ct al. (1996; Human retrotransposon encodes a conserved endonuclease required for retrotransposition, Cell 87: 905- 916) that the progenitor L1 elements encode a site-specific endonuclea se and that they generate copies that are inserted at these specific s ites. The analysis of retrotransposed LI elements within the alphoid d omains of the acrocentric chromosomes showed that a number of loci are shared among all five acrocentrics. This sheds light on the manner in which centromeric regions of these chromosomes are exchanging informa tion during evolution. (C) 1997 Academic Press.