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Sources and evolution of human Alu repeated sequences
R J Britten1, W F Baron, D B Stout
1Division of Biology, California Institute of Technology, Pasadena 91125.
Summary
Human DNA contains Alu repeats, which have evolved over millions of years. Older Alu repeats show distinct patterns, suggesting a series of ancient genes were their original sources via retroposition.
Area of Science:
- Molecular Evolution
- Genomics
- Primate Genetics
Background:
- Alu repeated sequences are abundant in the human genome, originating within the last 30 million years.
- These sequences exhibit varying degrees of similarity to the modern consensus sequence.
- Previous studies indicate that older Alu repeats possess unique sequence characteristics.
Purpose of the Study:
- To investigate the evolutionary history and origins of Alu repeated sequences in the human lineage.
- To identify distinct Alu subfamilies based on sequence divergence.
- To explore the potential source genes and mechanisms of Alu repeat propagation.
Main Methods:
- Comparative sequence analysis of Alu repeats at 26 diagnostic positions.
- Phylogenetic reconstruction to identify Alu subfamilies.
- Comparison of Alu sequences with the 7SL RNA sequence to infer ancestral relationships.
Main Results:
- Four distinct Alu subfamilies were identified based on conserved differences.
- Older Alu subfamilies exhibit greater sequence similarity to the ancestral 7SL RNA.
- Evidence suggests a series of conserved genes served as the source for Alu repeats through retroposition.
Conclusions:
- Alu repeat evolution in primates involved a succession of source genes.
- These source genes likely operated in overlapping relays during primate evolution.
- Retroposition of conserved genes is the probable mechanism for Alu family expansion.