Hyperrecombination in pneumococcus: A/G to C.G repair and requirement for DNA polymerase I.

Pasta F, Sicard MA
Mutation research (1994), Volume 315, Page 113
PubMed entry


During pneumococcal transformation, we had previously described that ...
During pneumococcal transformation, we had previously described that the ami36 mutation, which results from a C.G to A.T transversion, induces a large excess of wild-type recombinants in two point crosses. Upon donor-recipient DNA recombination, two heteroduplexes are generated by this mutation: A36/G+ and C+/T36. In two point crosses, hyperrecombination is observed only when transformation leads to the A/G mismatch. Here, we have studied the separate evolution of A36/G+ and C+/T36 heterozygotes created upon transformation of an ami36 mutant strain with artificial heteroduplex DNAs. We found that the A36/G+ mismatch leads to a preferential generation of wild-type progeny as compared with the complementary C+/T36 mismatch. This result suggests that A/G carrying transformants partly behave as wild-type homozygotes. The only way to account for such behavior is an excision repair correcting some A/G mispairs created upon transformation into C.G pairs. Moreover, we show that hyperrecombination triggered by ami36 is strongly reduced in a DNA polymerase I deficient strain. This strengthens the fact of DNA repair synthesis, which should be therefore prominently due to DNA polymerase I.




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