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Evolutionary selection against change in many Alu repeat sequences interspersed through primate genomes
1Division of Biology of the California Institute of Technology, Kerckhoff Marine Laboratory, Corona Del Mar 92625.
Summary
Human DNA's Alu repeats show suppressed mutations at protein-binding sites, indicating crucial, sequence-dependent genomic functions essential for primates. These findings suggest widespread functional roles for Alu elements beyond replication.
Area of Science:
- Genomics
- Molecular Biology
- Evolutionary Biology
Background:
- Alu repeats are abundant transposable elements in the human genome.
- Understanding mutations within these elements is key to their genomic role.
- Previous studies have not fully elucidated the functional significance of Alu sequence conservation.
Purpose of the Study:
- To investigate mutation patterns in human Alu repeats.
- To identify potential functional constraints on Alu sequences.
- To explore the implications of conserved sequences for primate genome function.
Main Methods:
- Sequencing of nearly full-length human Alu repeats (approx. 1500 instances).
- Comparative analysis of mutation rates at specific nucleotide positions.
- Statistical assessment of mutation suppression patterns and their correlation.
Main Results:
- Identified specific positions with significantly suppressed mutation rates ('suppressed changes').
- Observed clustering of these suppressed changes, correlating with predicted protein-binding sites.
- Demonstrated a strong joint probability of mutation absence at multiple correlated positions, exceeding random expectation.
- Ruled out Alu sequence replication as the cause of mutation suppression.
Conclusions:
- Mutation suppression suggests selective pressure acting on Alu sequences.
- Hundreds of thousands of Alu sequences likely possess genome-wide, sequence-dependent functions critical for primates.
- Alu elements may play roles in gene transcription regulation, as seen in known cases.