>>118770, >>118814

Spiegelman's Monster - RNA replicase
Spiegelman's Monster is the name given to an RNA chain of only 218 nucleotides that is able to be reproduced by the RNA replication enzyme RNA-dependent RNA polymerase, also called RNA replicase. It is named after its creator, Sol Spiegelman, of the University of Illinois at Urbana-Champaign who first described it in 1965.

AN EXTRACELLULAR DARWINIAN EXPERIMENT WITH A
SELF-DUPLICATING NUCLEIC ACID MOLECULE*
BY D. R. MILLS,t R. L. PETERSON, AND S. SPIEGELMAN
DEPARTMENT OF MICROBIOLOGY, UNIVERSITY OF ILLINOIS, URBANA
Communicated May 18, 1967

Summary.--Experiments were performed to explore the evolutionary consequences for a self duplicating nucleic acid molecule put under selection pressure for fast growth. As the experiment progressed, the rate of RNA synthesis increased and the product became smaller. By the 74th transfer the replicating molecule had eliminated 83 per cent of its original genome, becoming the smallest known self-duplicating entity. Aside from their intrinsic interest, such studies can provide insight into a number of central issues. Thus, they can tell us the smallest self-duplicating entity which can be constructed by such devices and provide much simpler objects for analyzing the replication process. Further, the sequences involved in the recognition mechanism between template and enzyme are enriched in the smaller molecules which evolve. Finally, these abbreviated molecules have a very high affinity for the replicase but are no longer able to direct the synthesis of virus particles. This feature opens up a novel pathway toward a highly specific device for interfering with viral RNA replication.

https://en.wikipedia.org/wiki/Directed_evolution
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC335620/pdf/pnas00677-0236.pdf