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Within-intron correlation with base composition of adjacent exons in different genomes
1Institute of Cytology, Russian Academy of Sciences, Tikhoretsky Avenue 4, 194064, St. Petersburg, Russia. aevin@mail.cytspb.rssi.ru
Gene
|October 10, 2001
Summary
Genome composition varies between introns and exons. Studies reveal selective forces favor intron-exon base similarity, especially near exons, challenging mutation bias as the sole driver of genome heterogeneity.
Area of Science:
- Genomics
- Molecular Biology
- Bioinformatics
Background:
- Genome composition exhibits significant heterogeneity, with variations observed between introns and exons.
- The correlation between intron and exon base composition is a key factor in understanding genome structure and evolution.
- Previous research indicated a general correlation between genome size and average intron length.
Purpose of the Study:
- To investigate the correlation between intron base composition and adjacent exon base composition across 34 species.
- To explore the factors influencing compositional differences within introns and their relationship with flanking exons.
- To re-evaluate the correlation between genome size and intron length using a larger dataset.
Main Methods:
- GC-percent analysis of 50 bp segments at intron margins and internal regions.
- Comparative analysis of correlation coefficients between intron and exon GC-percent.
- Statistical evaluation of differences in correlation for various species groups (homeotherms, cereals, anamniotes, invertebrates, dicots).
Main Results:
- A significantly higher correlation between intron margins and adjacent exon GC-percent was observed in homeotherms and cereals compared to the internal intron regions.
- Organisms with low within-intron correlation differences (anamniotes, invertebrates, dicots) exhibited greater local compositional heterogeneity (exon/intron GC-content contrast).
- The general positive correlation between genome size and average intron length was confirmed, though exceptions were noted within specific phylogenetic groups like cereals.
Conclusions:
- Selective forces appear to drive intron base composition towards similarity with adjacent exons in genomes with high global heterogeneity.
- This selective pressure is stronger in intron regions closer to exons, suggesting a functional role.
- The findings challenge mutational bias as the primary explanation for compositional genome heterogeneity and highlight the role of selection in intron-exon sequence alignment.