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. Author manuscript; available in PMC: 2017 May 1.
Published in final edited form as: Crit Rev Biochem Mol Biol. 2015 Dec 20;51(3):135–149. doi: 10.3109/10409238.2015.1125845

Figure 1.

Figure 1

Proposal for information flow in LUCA. LUCA contained proteins and the translation apparatus. Both RNA and DNA were probably present in LUCA, as inferred by homologous genes in all cell types that encode RNA polymerase, DNA ligase, ribonucleotide reductase and the RecA/Rad51 recombinase. In this diagram, RNA is the carrier of genomic information. The DNA is used as a substrate for homologous recombination (HR), RNA transcription, and to produce new copies of the RNA genome. RNA transcripts are decoded by the translation machinery that evolved the genetic code used in all cell types today. The RNA genome is replicated in simple fashion, requiring only a reverse transcriptase that first copies one strand, and then copies the second strand; no primase or helicase is required. A similar replication process is found in modern-day retroviruses (see color version of this figure at www.informahealthcare.com/bmg).