SEQUENTIAL INSERTION OF ALU FAMILY REPEATS INTO SPECIFIC GENOMIC SITES OF HIGHER PRIMATES

The presence of Alu family repeats is closely associated with interspe cies length polymorphisms of certain genomic regions among different h igher primates. By sequence analysis of cloned DNA, we show that one m ajor cause for the length difference between the gibbon adult alpha-gl obin locus and those of human, orangutan, and Old World monkeys is the existence of multimeric Alu family repeats. Triplet Alu family repeat s exist at two genomic sites of gibbon. Instead, singleton or doublet Alu family repeats are present at the orthologous positions in other h igher primates. Sequence comparisons suggest that these doublet and tr iplet Alu repeats have been created by successive insertion of differe nt singleton Alu repeat sequences, of almost-equal-to 300 bp, into the same genomic spot(s) during primate evolution. The approximate dates of insertion of these singleton Alu repeats support the concept of ove rlapping periods of active transposition or retroposition of Alu repea t subfamilies. This dynamic flow of Alu repeat sequences during primat e evolution into the adult alpha-globin loci, but not beta-globin-like loci, is consistent with the previous finding that R-banding regions of the primate chromosomes are enriched in Alu repeats.