Same-strand overlapping genes in bacteria: compositional determinants of phase bias

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• Same-strand overlapping genes exhibit a bias, with more phase-1 overlaps than phase-2 overlaps in bacterial genomes.
• Previous explanations involving genomic location or selection have limitations.
• A purely compositional model offers a more parsimonious explanation for this observed phase bias.

Purpose of the Study:

• To investigate whether codon composition explains the observed phase bias in same-strand overlapping genes.
• To test the hypothesis that frequencies of initiation and termination codons influence the number of overlapping genes.

Main Methods:

• Analysis of initiation- and termination-codon frequencies in bacterial genomes across different phases.
• Examination of amino acid frequencies and their relation to start codon formation.
• Correlation analysis between overlapping gene frequencies, codon usage, and genomic GC content.

Main Results:

• Initiation codons are significantly more abundant in phase 1 compared to phase 2.
• Termination codon frequencies do not significantly differ between phases.
• Amino acid frequencies and species-specific codon usage determine start codon frequencies, explaining the phase bias and correlating with GC content.

Conclusions:

• Compositional factors, specifically initiation codon frequencies, parsimoniously explain the phase bias in same-strand overlapping genes.
• The proposed model serves as a null model for neutral evolution, useful for testing selection hypotheses.
• This finding advances our understanding of the evolutionary mechanisms shaping gene organization.