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

Mutat Res. 1994 Sep;315(2):113-22. doi: 10.1016/0921-8777(94)90012-4.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Crosses, Genetic
  • DNA Polymerase I / metabolism*
  • DNA Repair / physiology*
  • DNA, Bacterial / genetics
  • Heterozygote
  • Kinetics
  • Nucleic Acid Heteroduplexes / physiology*
  • Point Mutation / genetics
  • Recombination, Genetic / genetics*
  • Streptococcus pneumoniae / genetics*
  • Streptococcus pneumoniae / growth & development
  • Transformation, Bacterial


  • DNA, Bacterial
  • Nucleic Acid Heteroduplexes
  • DNA Polymerase I