PHYLOGENETIC ISOLATION OF A HUMAN ALU FLOUNDER GENE - DRIFT TO NEW SUBFAMILY IDENTITY

A severe bottleneck in the size of the PV Alu subfamily in the common ancestor of human and gorilla has been used to isolate an Alu source g ene. The human PV Alu subfamily consists of about one thousand members which are absent in gorilla and chimpanzee DNA. Exhaustive library sc reening shows that there are as few as two PV Alus in the gorilla geno me. One is gorilla-specific, i.e., absent in the orthologous loci in b oth human and chimpanzee, suggesting the independent retrotranspositio nal activity of the PV subfamily in the gorilla lineage. The second of these two gorilla PV Alus is present in both human and chimpanzee DNA s and is the single PV Alu known to precede the radiation of these thr ee species. The orthologous Alu in gibbon DNA resembles the next older Alu subfamily. Thus, this Alu locus is originally templated by a non- PV source gene and acquired characteristic PV sequence variants by mut ational drift in situ, consequently becoming the first member and pres umptive founder of this PV subfamily.