How informational sequences emerge from random templated ligation

Reduction of the information entropy along with ever-increasing complexity are among the key signatures of life. Understanding the onset of such behavior in the early prebiotic world is essential for solving the problem of the origin of life. In Refs. [1,2] we studied a general problem of heteropolymers capable of template-assisted ligation based on Watson-Crick-like hybridization. The system is driven out of equilibrium by cyclic changes in the environment. We modeled [1] the dynamics of 2-mers, i.e., sequential pairs of specific monomers within the heteropolymer population. While the possible number of them is Z² (where Z is the number of monomer types), we observe that most of the 2-mers eventually get extinct, leaving no more than 2Z survivors. This leads to a dramatic reduction of the information entropy in the sequence space. This natural-selection-like process ultimately results in a limited subset of polymer sequences. Importantly, the set of surviving sequences depends on the initial concentrations of monomers and remains exponentially large (2^L reduced down from Z^L for chains of length L) in each of the realizations. Thus, an inhomogeneity in the initial conditions allows for a massively parallel search of the sequence space for biologically functional polymers, such as ribozymes. The problem has a surprising connection [3] to microbial ecology in which multiple exponentially growing species compete for two types of essential nutrients (e.g., C and N) analogous to Z right and left ends of polymers. Finally, I will describe a recent experimental realization of this system [4] demonstrating the emergence of highly structured sequence motifs, autocatalytic reaction networks, and a dramatic reduction of the information entropy.