Monophyletic Origin of Alu Elements in Primates |
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Authors: | Ewa Zi?tkiewicz Chantal Richer Daniel Sinnett Damian Labuda |
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Institution: | Centre de Recherche de l'H?pital Sainte-Justine, Centre de Cancérologie Charles Bruneau, Département de Pédiatrie de l'Université de Montréal, Montréal, Québec, H3T-1C5 Canada, CA
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Abstract: | To get insight into the early evolution of the primate Alu elements, we characterized sequences of these repeats from the
Malagasy prosimians, lemurs (Lemuridae) and sifakas (Indriidae), as well as from galagos (Lorisidae). These sequences were
compared with the oldest Alu species known from the human genome: dimeric Alu J and S and free Alu monomers. Our analysis
indicates that about 60 Myr ago, before the prosimian divergence, free left and right monomers formed an Alu heterodimer connected
by a 19-nucleotide-long A-rich linker. The resulting elements successfully propagated in diverging primate lineages until
about ∼20 Myr ago, conserving similar sequence features and essentially the same Alu RNA secondary structure. We suggest that
until that time the same ``retropositional niche', molecular machinery making possible the proliferation by retroposition,
constrained the evolution of Alu elements in extant primate species. These constraints became subsequently relaxed. In the
Malagasy prosimians the dimeric Alu continued to amplify after acquiring a 34- to 36-nucleotide extension of their linker
segment, whereas in the galago genome the ``retropositional niche' was occupied by novel short elements.
Received: 1 December 1997 / Accepted: 30 January 1998 |
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Keywords: | : Short interspersed sequence elements (SINES) — Retroposition — Alu evolution — Alu RNA folding — Primate lineages — Prosimians — Genomic repeats |
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