Processive RNA polymerization and promoter recognition in an RNA World.

Early life is thought to have required the self-replication of RNA by RNA replicases. However, how such replicases evolved and subsequently enabled gene expression remains largely unexplored. We engineered and selected a holopolymerase ribozyme that uses a sigma factor-like specificity primer to first recognize an RNA promoter sequence and then, in a second step, rearrange to a processive elongation form. Using its own sequence, the polymerase can also program itself to polymerize from certain RNA promoters and not others. This selective promoter-based polymerization could allow an RNA replicase ribozyme to define "self" from "nonself," an important development for the avoidance of replicative parasites. Moreover, the clamp-like mechanism of this polymerase could eventually enable strand invasion, a critical requirement for replication in the early evolution of life.