A Model for the Achievement of Accuracy in Biology and Economy

Abstract

High levels of accuracy are difficult to achieve, yet they are critically important for the correct function of living systems. In molecular biology, where the problem is mostly one of accurate transfer of information, various systems have been developed to reach the required level of accuracy. An interesting case is provided by the mechanism of DNA replication. It appears that in bacteria, the enzyme which polymerizes the nucleotides into a new chain of DNA also presents an exonuclease activity which selectively excises mismatched nucleotides (Brutlag and Romberg, 1972). In eukaryotes, where the purified DNA polymerases have no nuclease activity, the “proofreading” seems to be done by a separate exonuclease which is responsible for the removal of incorrect nucleotides (Spadari, Villani and Radman, in prep.). This suggests that the replication of DNA is a two-step process : first the DNA polymerase catalyzes the addition of a new nucleotide on the growing DNA chain ; then a nuclease checks the fidelity of the process, thereby increasing the initial level of accuracy. A “proofreading” mechanism also seems to operate during the synthesis of proteins (Ninio, 1974).