Evolution of the cryptic FMR1 CGG repeat.
We have sequenced the 5' untranslated region of the orthologous FMR1 gene from 44 species of mammals. The CGG repeat is present in each species, suggesting conservation of the repeat over 150 million years of mammalian radiation. Most mammals possess small contiguous repeats (mean number of repeats = 8.0 +/- 0.8), but in primates, the repeats are larger (mean = 20.0 +/- 2.3) and more highly interrupted. Parsimony analysis predicts that enlargement of the FMR1 CGG repeat beyond 20 triplets has occurred in three different primate lineages. In man and gorilla, AGG interruptions occur with higher-order periodicity, suggesting that historical enlargement has involved incremental and vectorial addition of larger arrays demarcated by an interruption. Our data suggest that replication slippage and unequal crossing over have been operative during the evolution of this repeat.
Eichler
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EE
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA.
Kunst
C B
CB
Lugenbeel
K A
KA
Ryder
O A
OA
Davison
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D
Warren
S T
ST
Nelson
D L
DL
D000818:Animals; D001483:Base Sequence; D019143:Evolution, Molecular; D051860:Fragile X Messenger Ribonucleoprotein 1; D008322:Mammals / Q000235:genetics*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins; D011323:Primates / Q000235:genetics; D016601:RNA-Binding Proteins; D012091:Repetitive Sequences, Nucleic Acid
D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins