ALU REPEATS - A SOURCE FOR THE GENESIS OF PRIMATE MICROSATELLITES

As a result of their abundance, relatively uniform distribution, and h igh degree of polymorphism, microsatellites and minisatellites have be come valuable tools in genetic mapping, forensic identity testing, and population studies. In recent years, a number of microsatellite repea ts have been found to be associated with ALu interspersed repeated DNA elements. The association of an Alu element with a microsatellite rep eat could result hom the integration of an ALu element within a preexi sting microsatellite repeat. Alternatively, ALu elements could have a direct role in the origin of microsatellite repeats. Errors introduced during reverse transcription of the primary transcript derived hom an Alu ''master'' gene or the accumulation of random mutations in the mi ddle A-rich regions and oligo(dA)-rich tails of Alu elements after ins ertion and subsequent expansion and contraction of these sequences cou ld result in the genesis of a microsatellite repeat, We have tested th ese hypotheses by a direct evolutionary comparison of the sequences of some recent Alu elements that are found only in humans and are absent from nonhuman primates, as well as some older Alu elements that are p resent at orthologous positions in a number of nonhuman primates. The origin of ''young'' Alu insertions, absence of sequences that resemble microsatellite repeats at the orthologous loci in chimpanzees, and th e gradual expansion of microsatellite repeats in some old Alu repeats at orthologous positions within the genomes of a number of nonhuman pr imates suggest that Ab elements are a source for the genesis of primat e microsatellite repeats. (C) 1995 Academic Press, Inc.