The first universal common ancestor (FUCA) is a proposed non-cellular entity that was the earliest organism with a genetic code capable of biological translation of RNA molecules into peptides to produce proteins.
[1] Long before the appearance of compartmentalized biological entities like FUCA, life had already begun to organize itself and emerge in a pre-cellular era known as the RNA world.
[1] The first genes of FUCA were most likely encoding ribosomal, primitive tRNA-aminoacyl transferases and other proteins that helped to stabilize and maintain biological translation.
[4] This genetic code was for the first time capable to organize an ordered interaction between nucleic acids and proteins through the formation of a biological language.
[4] This caused pre-cellular open systems to then start to accumulate information and self-organize, producing the first genomes by the assembly of biochemical pathways, which probably appeared in different progenote populations evolving independently.
[3] Progenotes (also called ribocytes or ribocells)[7][8][9] are semi-open or open biological systems capable of performing an intense exchange of genetic information, before the existence of cells and LUCA.
[6] In Carl Woese's Darwinian threshold period of cellular evolution, the progenotes are also thought to have had RNA as informational molecule instead of DNA.
[17] As ribocytes used RNA to store their genetic info,[17] viruses may initially have adopted DNA as a way to resist RNA-degrading enzymes in the host ribocells.