Error thresholds for self- and cross-specific enzymatic replication

The information content of a non-enzymatic self-replicator is limited by Eigen s error threshold Presumably enzymatic replication can maintain higher complexity but in a competitive environment such i replicator is faced with two problems related to its twofold role as enzyme and substrate as enzyme it should replicate itself rather than wastefully copy non-functional substrates and as substiate it should preferably be replicated by superior enzymes instead of less-efficient mutants Because specific recognition can enforce these propensities we thoroughly analyze an idealized quasispecies model for enzymatic replication with replication rates that are either a decreasing (self specific) or increasing (cross-specific) function of the Hamming distance between the recognition or tag sequences of enzyme and substrate We find that very weak self-specificity suffices to localize a population about a master sequence and thus to preserve its information while simultaneous localization about complementary sequences in the cross-specific case is more challenging A surprising result is that stronger specificity constraints allow longer recognition sequences because the populations are better localized Extrapolating from experimental data we obtain rough quantitative estimates for the maximal length of the recognition or tag sequence that can be used to reliably discriminate appropriate and infeasible enzymes and substrates respectively (C) 2010 Elsevier Ltd All rights reserved