The Last Universal Common Ancestor of Ribosome-Encoding Organisms: Portrait of LUCA

Area of Science:

• Origin of Life Studies
• Evolutionary Biology
• Genomics

Background:

• The existence of the Last Universal Common Ancestor (LUCA) is inferred from cellular evolution and binary cell division.
• Early life evolved from the origin of life through an RNA world to LUCA and subsequent diversification.
• LUCA's biosphere was a product of extensive cellular evolution.

Purpose of the Study:

• To reconstruct a parsimonious scenario for LUCA's molecular fabric and metabolic capabilities.
• To explore the implications of Eukarya's phylogenetic position on LUCA's characteristics.
• To propose a hypothesis for the origin of DNA viruses from an RNA-based LUCA.

Main Methods:

• Phylogenomic analyses to infer LUCA's molecular composition and traits.
• Comparative genomics to understand the presence/absence of key enzymes like reverse gyrase.
• Analysis of evolutionary tempo and patterns of viral distribution.

Main Results:

• LUCA likely possessed a simpler molecular structure than extant organisms, facilitating a faster evolutionary tempo.
• LUCA may have had an RNA genome and lacked ATP synthase but performed basic metabolism and protein synthesis.
• Phylogenetic data suggest LUCA lacked reverse gyrase, indicating it was a mesophile or moderate thermophile.

Conclusions:

• LUCA's characteristics were simpler, contributing to rapid early evolution.
• The phylogenetic placement of Eukarya impacts the potential presence of features like the spliceosome in LUCA.
• DNA viruses likely emerged after LUCA, during the diversification of the three domains, from an RNA-based ancestor.