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Selection against frameshift mutations limits microsatellite expansion in coding DNA
1Department of Biology, University of California at San Diego, La Jolla, California 92093-0116 USA.
Genome Research
|January 25, 2000
Summary
Microsatellite repeat sequences show different enrichment patterns in eukaryotic coding and noncoding DNA. Noncoding regions have excesses of all repeat types, while coding regions favor specific triplet repeats, suggesting strong selective pressures.
Area of Science:
- Genomics
- Molecular Evolution
Background:
- Microsatellites, or repetitive DNA sequences, are common in eukaryotes and thought to arise from replication slippage.
- Enrichment quantifies microsatellite excess over random nucleotide association.
Purpose of the Study:
- To compare microsatellite enrichment in coding versus noncoding DNA across seven eukaryotic clades.
- To investigate the factors influencing microsatellite distribution in different genomic contexts.
Main Methods:
- Comparative analysis of microsatellite frequencies in coding and noncoding sequences.
- Examination of repeat types (mono- to hexanucleotide) and their enrichment levels.
- Statistical assessment of enrichment patterns across eukaryotic clades.
Main Results:
- Noncoding regions exhibit excesses of all microsatellite types, with enrichment scaling exponentially with repeat length.
- Coding regions show significantly lower frequencies of non-triplet repeats compared to noncoding regions.
- Tri- and hexanucleotide repeats are consistently enriched in both coding and noncoding sequences.
Conclusions:
- Differences in microsatellite enrichment between coding and noncoding DNA are significant and conserved across eukaryotes.
- Strong selection against frameshift mutations in coding regions likely explains the rarity of non-triplet repeats.
- Mutation pressure appears to be the primary driver for the enrichment of tri- and hexanucleotide repeats in coding DNA.
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