Fig. 1. Recombination system to study instability of Alu repeats in yeast. Alu repeats (open arrows) were inserted into the BamHI site of the LYS2 gene (black arrows). The Alu arrows describe the direction of transcription by RNA polymerase III; the arrowhead corresponds to the 3′ poly(A) tail (Schmid, 1996). The positions of nucleotide changes relative to the human-specific (HS) Alu consensus sequence (blank open arrow) are indicated as vertical lines within the arrows. The length of the spacer region separating the Alu repeats and the extent of homology in the Alu pairs are shown. The distances between the lys2-8 mutation (white rectangle) and the Alu insertion site are indicated (610 bp). The ‘X’ denotes a recombination event generating a wild-type LYS2 allele.