Figure 1.

(a) Principle of short-patch CSR (spCSR). spCSR is based on a simple feedback loop, in which a polymerase replicates a short segment (a patch) of its own encoding gene as defined by the flanking primer selection (half arrows). Compartmentalization in a water-in-oil emulsion serves to isolate individual self-replication reactions from each other. In such a system adaptive gains translate into genetic amplification of the encoding gene. Two independent emulsion compartments are shown. Polymerases (Pol1 (left compartment)) that are capable of utilizing Cy5-dCTP are able to replicate, i.e., produce “offspring”, while polymerases like Pol2 (right compartment) that are unable to utilize it disappear from the gene pool. (b) Structures of Cy3-dCTP (left) and Cy5-dCTP (right), showing the cyanine dyes attached to the 5′ position of cytidine via a flexible linker. Cy3-dCTP differs from Cy5-dCTP only by the length of the polymethine bridge separating the indolene heterocycles. PPP stands for triphosphate.