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Bacterial actins? An evolutionary perspective
Russell F Doolittle1, Amanda L York
1Center for Molecular Genetics, University of California, San Diego, La Jolla 92093-0634, USA. rdoolittle@ucsd.edu
Summary
The bacterial mreB protein is homologous to eukaryotic actin, challenging the idea that a cytoskeleton is unique to eukaryotes. This finding suggests a deeper evolutionary history for cytoskeletal components than previously understood.
Area of Science:
- Cell Biology
- Evolutionary Biology
- Microbiology
Background:
- The presence of a cytoskeleton in eukaryotes and its absence in prokaryotes has been considered a fundamental distinction between these life domains.
- This distinction has supported theories on eukaryotic evolution, including phagocytosis of prokaryotes and subsequent organelle development.
Purpose of the Study:
- To investigate the evolutionary origins of cytoskeletal components.
- To determine if homologs of eukaryotic cytoskeletal proteins exist in prokaryotes.
Main Methods:
- Comparative sequence analysis of eukaryotic actin and bacterial mreB protein.
- Examination of evolutionary histories of these homologous proteins.
Main Results:
- Compelling evidence indicates that the bacterial mreB protein is a homolog of eukaryotic actin.
- Both proteins exhibit similar functional behaviors.
- Sequence comparisons reveal significantly divergent and extended evolutionary histories for actin and mreB compared to other shared proteins.
Conclusions:
- The findings challenge the conventional view of the cytoskeleton as exclusively eukaryotic.
- The evolutionary history of cytoskeletal components is more complex and ancient than previously assumed.
- This discovery has implications for understanding early eukaryotic cell evolution and the origin of organelles.