Base mismatches and mutagenesis: how important is tautomerism?

Abstract

The majority of mismatches have C 1′-C 1′ distances that are very close to the standard distance found in Watson-Crick base pairs. This means that there is minimal disturbance of the double helix, which in any case is very variable in detail 16. If the C 1′-C 1′ distance is the most important geometrical facet of the bases, then it seems likely, since a pyrimidine or purine itself presents a very different geometry, that the enzyme can cope with any difference in the backbone due to its inherent flexibility. Tautomerism cannot be excluded but it would seem that it is the harder case to prove. What is needed now are accurate measurements of tautomer ratios by modern techniques. The older values were recognized at the time to be very approximate because of inherent assumptions. This review will hopefully stimulate research in understanding the slow majestic pace of evolution at the molecular level.