Determining divergence times with a protein clock: update and reevaluation

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Genomics

Background:

• Organismal divergence times are typically estimated using molecular sequence comparisons.
• Previous studies relied on amino acid sequence data to infer evolutionary relationships.
• Complete genome sequences offer new insights into ancient evolutionary events.

Purpose of the Study:

• To reanalyze organismal divergence times using improved methods and new genomic data.
• To investigate the phylogenetic placement of archaebacteria within the Tree of Life.
• To refine estimates of divergence times for major bacterial and archaeal lineages.

Main Methods:

• Amino acid sequence comparison with a refined distance measure accounting for substitution rate variation.
• Analysis of complete genome sequences from eubacteria and archaebacteria.
• Phylogenetic analysis to determine the relationships between different organismal groups.

Main Results:

• Archaebacterial sequences often appear as outliers or mixed with eubacterial orthologs, contradicting their usual clustering with eukaryotes.
• A significant portion of archaebacterial sequences in eukaryotes may originate from early eubacterial endosymbionts (~2 billion years ago).
• Eubacterial groups (cyanobacteria, Gram-positive, Gram-negative) and eukaryotes likely diverged around the same time, while archaebacteria and eubacteria diverged 3-4 billion years ago.

Conclusions:

• The Tree of Life may require revision regarding the placement and origin of archaebacteria.
• Endosymbiotic gene transfer from eubacteria played a crucial role in early eukaryotic evolution.
• Divergence times for early life forms can be more accurately estimated with advanced genomic and bioinformatic approaches.