Population dynamics of ribozymes during in vitro selection

Ribozymes are central to models of RNA-based primordial life. Understanding how ribozymes emerge from RNA populations under changing selection pressures is essential for reconstructing early biochemical systems. In vitro selection has been instrumental in isolating ribozymes from combinatorial populations; however, their population dynamics during selection remains poorly characterized. By analyzing high-throughput sequencing data from all eight rounds of an in vitro selection experiment, consisting of over 5 million unique sequences, we were able to track how sequences rise and fall in abundance during selection. We found that the most abundant sequences emerged early and maintained their dominance, suggesting that only a few cycles of selection-amplification may be sufficient to isolate well-adapted ribozymes. Nucleotide conservation analysis of the dominant ribozyme family and experimental characterization of rare variants indicated that abundance did not always predict activity. Our analyses show that sequence complementarity with the substrate emerged as a common feature in as early as the first round, highlighting early convergence of diverse sequence populations on a beneficial catalytic strategy. Our work presents the most detailed description of ribozyme population dynamics during an in vitro selection experiment and provides a high-resolution view of how RNA sequences compete for survival and propagation.