Misinsertion frequency

Fersht. A.R. Knill-Jones, J.W. Tsui. W.-C. Kinetic basis of spontaneous mutation. Misinsertion frequencies, proofreading specificities and cost of proofreading by DNA polymerases of Escherichin coli. J. Mol. Biol. 1982. 156, 37-51. 

The frequency of these misinsertions is quite high, being about 8% in the more isotactic samples. This value results in an average stereoblock length of only about 12 units and explains the low melting point ( 60 °C) and low crystallinity (<20%) observed for this material and its physical properties, which are... 

Polt/ and Polt are characterized not only by high levels of nucleotide misinsertion but also by their relatively high efficiency of mismatch extension compared to classical DNA polymerases. The range of single mismatch extension frequencies by Polt and both yeast and human Pol are similar... 

The reader will note that the regiochemistry for the insertion of olefins in Scheme 2 and elsewhere is presumed to be that which causes carbon 1 of the 0 -olefin to be boimd to the metal this is denoted 1,2-insertion, while the case in which the monomer inserts with opposite arrangement is known as 2,1-insertion or regioerror. While chain-end stndies have shown 1,2-insertion to be the dominant regiochemistry, misinsertion may exert an influence upon the rates of chain transfer or ultimate polymer properties out of proportion to its frequency. Regio-chemical inversion seems to be rather prevalent in polypropylene produced by mono-Cp titanocene catalysts (153). 

Several catalysts have been found to produce iPP through the chain-end control mechanism. These include the Cp2TiR2/MAO systems (Cp = C5H5 or substituted Cp R = Ph or Cl) " and (pyridyldiimine)FeCl2/modified methylaluminoxane catalysts. Low polymerization temperatures are required to achieve moderate isotacticity with both classes of catalysts. The frequency of misinsertions produces an average stereoblock length of less than 16 units, the minimum required for... 

Incorrect nucleotides that traverse the first-stage physical discrimination by a polymerase may get inserted but do not accumulate off the polymerase. Misinser-tion results in a slower dissociation of the incorrect DNA product from the enzyme, providing a higher probability for the editing exonuclease to function and thus a fidelity increase of 4- to 61-fold. Finally, misinserted nucleotides are not locked in by addition of the next correct dNTP. The nucleotide sealing action occurs extremely slowly, resulting in a further fidelity increase of 6- to 340-fold. Ideal functioning of the triple-check process would lead to an error frequency of 10 °, close to the maximum fidelity estimated for in vivo DNA replication. 

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