DNA structure constraint is probably a fundamental factor inducing CpG deficiency in bacteria

Area of Science:

• Genomics
• Bioinformatics
• Molecular Biology

Background:

• CpG dinucleotide deficiency in genomes is often attributed to DNA methylation.
• This methylation hypothesis inadequately explains CpG deficiency observed in bacterial genomes.
• An alternative hypothesis proposes DNA structure constraints as a cause.

Purpose of the Study:

• To investigate the role of DNA structure constraints in CpG deficiency in bacterial genomes.
• To examine context-dependent counterselection of specific DNA patterns.
• To explore the relationship between genome-wide GC content and CpG deficiency.

Main Methods:

• Comparative analysis of real bacterial genomes and second-order Markov artificial genomes.
• Identification and analysis of underrepresented DNA sequence patterns.
• Random sequence simulations to correlate pattern occurrences with GC content and CpG dinucleotides.

Main Results:

• The TTCGAA pattern, a core structure, is underrepresented in low GC content bacterial genomes, irrespective of CpG levels.
• Counterselection is context-dependent, contrasting with the AACGTT pattern.
• Nine underrepresented patterns, primarily TTCGNA and TTCGAN, were identified as potential inducers of DNA structure constraint.
• A strong correlation between GC content and CpG deficiency was observed, with CpG dinucleotides often trapped within these restricted patterns.

Conclusions:

• DNA structure constraints, rather than solely DNA methylation, significantly contribute to CpG deficiency in bacteria.
• The degree of counterselection against specific DNA patterns is influenced by the global GC content of a genome.
• The findings provide a new perspective on the evolutionary forces shaping bacterial genome composition.