Evolutionary expansion of structurally complex DNA sequences.

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• The frequency of G(3+)N(1-7)G(3+)N(1-7)G(3+)N(1-7)G(3+) motifs has notably increased across eumetazoa with available genomic sequences.
• This expansion significantly exceeds frequencies expected in random genomes, indicating positive selective pressure.

Purpose of the Study:

• To investigate the evolutionary drivers and functional implications of the rapid expansion of G(3+)N(1-7)G(3+)N(1-7)G(3+)N(1-7)G(3+) motifs in eumetazoan genomes.
• To explore the potential role of these motifs in non-B DNA structure formation and epigenetic regulation.

Main Methods:

• Comparative genomics analysis of complete genomic sequences from various eumetazoan species.
• Bioinformatic assessment of motif frequency against random sequence expectations.
• Literature review on non-B DNA structures (quadruplexes, triplexes, hairpins) and their formation/suppression mechanisms.

Main Results:

• The observed frequency of G(3+)N(1-7)G(3+)N(1-7)G(3+)N(1-7)G(3+) motifs is consistently higher than predicted by random chance across studied genomes.
• The expansion is facilitated by cellular systems that suppress non-B DNA conformations during replication and repair, alongside proteins that promote unusual DNA structures.
• Evidence suggests positive selection acting on these motifs, implying functions beyond potential negative impacts on genome stability.

Conclusions:

• The proliferation of G(3+)N(1-7)G(3+)N(1-7)G(3+)N(1-7)G(3+) motifs is a significant evolutionary trend in eumetazoa, driven by positive selection.
• These motifs contribute to genome evolution by increasing the repertoire of nucleic acid structural states available for epigenetic modifications.
• Cellular machinery plays a crucial role in enabling and potentially exploiting the formation of non-B DNA structures conferred by these motifs.