Protein and nucleic acid together: a mechanism for the emergence of biological selection.

The ability of RNA to both replicate and carry out enzymic functions has led to the proposal that an 'RNA-world' preceded the emergence of protein function in pre-biotic evolution. This order of function requires a key transition in which replicating RNA-molecules 'breakout' and recruit protein function. Here I propose a mechanism for the co-evolution of protein and nucleic acids as replicating entities from the earliest stages of pre-biotic development. In the model, amyloid protein fibres provide a protective support and compartment for nucleic acids. In turn, replicating nucleic acids stimulate fibre growth at amyloid free ends. Nucleic acid-amyloid fibre combinations are proposed to lengthen and then break through hydrostatic shear, exposing new amyloid free ends. This process would distribute stable replicating complexes throughout the primordial environment. The model provides a route into the RNA-protein world without the need for a distinct 'breakout' transition.