J. Biol. Chem., Vol. 259, Issue 19, 11713-11717, 10, 1984
On the molecular basis of transition mutations. Frequency of forming 2- aminopurine-cytosine base mispairs in the G X C----A X T mutational pathway by T4 DNA polymerase in vitro
DN Mhaskar and MF Goodman
An in vitro model system including wild-type T4 DNA polymerase, the
mutagenic nucleotide analogue 2-aminopurine deoxyribonucleoside
triphosphate, and poly[d(A,C)] X oligo(dT) poly(dC) X oligo(dG)
template-primers is used to measure the frequency of 2-aminopurine X
cytosine base mispairs formed in the G X C----A X T mutational pathway.
Incorporation and turnover of the analogue into DNA is dependent on the
presence of cytosine on the template strand and is reduced significantly in
the presence of dGTP. 2-Aminopurine X cytosine mispairs are observed to
occur at a 2-3 order of magnitude greater frequency than adenine X cytosine
mispairs. The frequency of inserting 2-aminopurine deoxyribonucleoside
monophosphate in place of dGMP opposite template cytosine sites is about
3-6% when either strong or weak base-stacking partners are present on the
primer strand. However, enzymatic proofreading of the mispair strongly
depends on base-stacking partners. Greater than 85% of misinserted
2-aminopurine deoxynucleotides are excised whenever the mispairs are formed
next to 5'-primer thymine sites. A 5-fold reduction in proofreading
frequency occurs when the mispair is formed with 2-aminopurine
deoxynucleoside monophosphate stacked adjacent to a 5'-primer guanine. The
frequency of 2-aminopurine X cytosine base mispair formation in the G X
C----A X T pathway is similar to that found previously in the A X T----G X
C pathway (Watanabe, S. M., and Goodman, M.F. (1981) Proc. Natl. Acad. Sci.
U.S.A. 78, 2864-2868). We propose a criterion for base selection by DNA
polymerase to account for the unexpected similarity in base mispairing
rates in the two transition pathways.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
