The compositional distribution of coding sequences and DNA molecules in humans and murids

Area of Science:

• Genomics
• Molecular Evolution
• Comparative Genomics

Background:

• Mammalian genomes exhibit variations in DNA composition, specifically Guanine-Cytosine (GC) content.
• Previous studies have noted differences in compositional distributions across species, but detailed comparisons between rodents and humans were lacking.

Purpose of the Study:

• To investigate the differences in compositional distributions of coding and DNA sequences between murids (mice and rats) and humans.
• To understand the evolutionary mechanisms driving these compositional variations.

Main Methods:

• Analysis of compositional distributions of coding sequences and DNA molecules (50-100 kb) in murids and humans.
• Comparison of GC levels across all three codon positions in homologous genes.
• Linear regression analysis of GC levels between homologous genes from different species.
• Density gradient centrifugation to analyze DNA fractions.

Main Results:

• Murids display significantly narrower GC compositional distributions for both coding sequences and DNA molecules compared to humans.
• Differences in GC levels at all three codon positions contribute to variations in codon usage and amino acid composition.
• A conserved order of GC levels in homologous genes was observed between murids and humans, indicated by high correlation coefficients.
• Similar linear relationships were found for corresponding DNA fractions, suggesting genome-wide compositional changes.

Conclusions:

• Orderly compositional changes have occurred in both coding and non-coding sequences since the divergence of murids and humans.
• Directional fixation of mutations, driven by selective pressures acting on the genome, likely underlies these observed compositional differences.