A model for genesis of transcription systems

Repeating sequences generated from RNA gene fusions/ligations dominate ancient life, indicating central importance of building structural complexity in evolving biological systems. A simple and coherent story of life on earth is told from tracking repeating motifs that generate α/β proteins, 2-double-Ψ-β-barrel (DPBB) type RNA polymerases (RNAPs), general transcription factors (GTFs), and promoters. A general rule that emerges is that biological complexity that arises through generation of repeats is often bounded by solubility and closure (i.e., to form a pseudo-dimer or a barrel). Because the first DNA genomes were replicated by DNA template-dependent RNA synthesis followed by RNA template-dependent DNA synthesis via reverse transcriptase, the first DNA replication origins were initially 2-DPBB type RNAP promoters. A simplifying model for evolution of promoters/replication origins via repetition of core promoter elements is proposed. The model can explain why Pribnow boxes in bacterial transcription (i.e., (-12)TATAATG(-6)) so closely resemble TATA boxes (i.e., (-31)TATAAAAG(-24)) in archaeal/eukaryotic transcription. The evolution of anchor DNA sequences in bacterial (i.e., (-35)TTGACA(-30)) and archaeal (BRE(up); BRE for TFB recognition element) promoters is potentially explained. The evolution of BRE(down) elements of archaeal promoters is potentially explained.