EMERGENCE OF SYMBIOSIS IN PEPTIDE SELF-REPLICATION THROUGH A HYPERCYCLIC NETWORK

Symbiosis is an association between different organisms that leads to a reciprocal enhancement of their ability to survive, Similar mutually beneficial relationships can operate at the molecular level in the fo rm of a hypercycle, a collective of two or more self-replicating speci es interlinked through a cyclic catalytic network(1-5). The superposit ion of cross-catalysis onto autocatalytic replication integrates the m embers of the hypercycle into a single system that reproduces through a second-order (or higher) form of nonlinear autocatalysis. The hyperc ycle population as a whole is therefore able to compete more efficient ly for existing resources than any one member on its own. In addition, the effects of beneficial mutations of any one member are spread over the entire population, The formation of hypercycles has been suggeste d as an important step in the transition from inanimate to living chem istry(6), and a large number of hypercycles are expected to be embedde d within the complex networks of living systems(7). But only one natur ally occurring hypercycle has been well documented(8), while two autoc atalytic chemical systems may contain vestiges of hypercyclic organiza tion(9,10). Here we report a chemical system that constitutes a dear e xample of a minimal hypercyclic network, in which two otherwise compet itive self-replicating peptides symbiotically catalyse each others' pr oduction.