From simple bacterial and archaeal replicons to replication N/U-domains

Area of Science:

• Genomics
• Molecular Biology
• Evolutionary Biology

Background:

• The Replicon Theory, proposed 50 years ago, describes genome organization into replicons.
• Replication mechanisms vary across bacteria, archaea, and eukarya.

Observation:

• Eukaryotic replicons exhibit less specific and efficient replication initiation compared to prokaryotes.
• ~50% of the human genome is organized into ~1,500 megabase-sized replication domains.
• These domains display characteristic U-shaped replication timing and N-shaped replication fork polarity gradients.

Findings:

• Replication domains are self-interacting chromatin segments replicated from borders inward.
• Replication occurs via cascades of origin firing, potentially involving fork-stimulated initiation.
• Conserved replication patterns in mammalian germlines lead to N-shaped nucleotide compositional skew over evolutionary time.

Implications:

• This replication organization is evolutionarily conserved yet developmentally plastic.
• Replication patterns actively drive mammalian genome evolution.
• Understanding these domains provides insights into genome stability and evolutionary processes.