Chromosomal location and evolutionary rate variation in enterobacterial genes

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The rate of DNA sequence evolution is not uniform across all genes within a genome.
• Previous studies suggest gene expression levels influence evolutionary rates due to codon usage bias.

Purpose of the Study:

• To investigate the factors affecting the basal rate of DNA sequence evolution in enterobacteria.
• To determine the relationship between gene expression, synonymous codon usage, and chromosomal location on DNA divergence.

Main Methods:

• Comparative analysis of DNA sequences between Escherichia coli and Salmonella typhimurium.
• Focus on "silent" DNA sites to minimize the impact of amino acid changes.
• Statistical analysis correlating gene divergence with gene expression levels and chromosomal position relative to oriC.

Main Results:

• Significant variation in DNA sequence divergence was observed among different genes, even at silent sites.
• Gene divergence is strongly correlated with the level of gene expression, indicating selection on synonymous codon usage.
• For genes with weak expression constraints, divergence is also linked to chromosomal location; genes farther from oriC exhibit approximately double the mutation rate of genes near oriC.

Conclusions:

• Both gene expression levels and chromosomal location influence DNA sequence evolution in enterobacteria.
• The proximity to the origin of replication (oriC) appears to be a significant factor in mutation rate variation.
• These findings highlight the complex interplay of selective pressures and regional genomic factors shaping bacterial genome evolution.