Alu master copies serve as the drivers of differential SINE transposition in recent primate genomes

Alu elements, averaging ~300bp in length, are a family of primate-specific short intersperse nuclear elements (SINEs) with more than one million copies and contributing to ~11% of primate genomes. Despite mostly being shared among primates, our recent study revealed highly differential recent Alu transposition among the genomes of primates from Hominidae and Cercopithecidae families. To understand the underlying mechanism, we analyzed six primate genomes and revealed species- and lineage-specific Alu profile exclusively defined by AluY composition. Among all Alus from the 6 genomes, we identified 5401 Alu master copies with 99% being from the AluY subfamily. The numbers of Alu master copies are positively correlated to the number of AluY elements in the genomes with the baboon genome having the largest number of most recent Alu master copies at high activities, while the crab-eating macaque genome having a low number of Alu master copies with low activity. Furthermore, the expression level of Alu master copies is positively correlated with their transposition activity. Our results support the concept that Alu transposition in primate genomes is driven by a small number of master copies, the number and relative activity of which contribute to the differential Alu transposition in recent primate genomes.