A similar method of obtaining new deoxyribozymes is through in vitro evolution. Though this term is often used interchangeably with in vitro selection, in vitro evolution more appropriately refers to a slightly different procedure in which the initial oligonucleotide pool is genetically altered over subsequent rounds through genetic recombination or through point mutations. For point mutations, the pool can be amplified using error-prone PCR to produce many different strands of various random, single mutations. As with in vitro selection, the evolved strands with increased activity will tend to dominate the pool after multiple selection steps, and once a sufficient catalytic activity is reached, the pool can be sequenced to identify the most active strands.
The initial pool for in vitro evolution can be derived from a narrowed subset of sequence space, such as a certain round of an in vitro selection experiment, which is sometimes also called in vitro reselection. The initial pool can also be derived from amplification of a single oligonucleotide strand. As an example of the latter, a recent study showed that a functional deoxyribozyme can be selected through in vitro evolution of a non-catalytic oligonucleotide precursor strand. An arbitrarily chosen DNA fragment derived from the mRNA transcript of bovine serum albumin was evolved through random point mutations over 25 rounds of selection. Through deep sequencing analysis of various pool generations, the evolution of the most catalytic deoxyribozyme strand could be tracked through each subsequent single mutation.
This first successful evolution of catalytic DNA from a non-catalytic precursor could provide support for the RNA World hypothesis. In another recent study, an RNA ligase ribozyme was converted into a deoxyribozyme through in vitro evolution of the inactive deoxyribo-analog of the ribozyme. The new RNA ligase deoxyribozyme contained just twelve point mutations, two of which had no effect on activity, and had a catalytic efficiency of approximately 1/10 of the original ribozyme, though the researches hypothesized that the activity could be further increased through further selection.
This first evidence for transfer of function between different nucleic acids could provide support for various pre-RNA World hypotheses.