SUMMARY: Exponentially growing PAM5717 is radiation-sensitive, does not carry out ‘slow’ repair of single-strand DNA breaks and shows substantial DNA degradation after gamma-irradiation. When chloramphenicol is present for 90 min before and after gamma-irradiation, survival is enhanced, DNA degradation is minimal and single-strand DNA breaks are repaired both in PAM5717 and the radiation-resistant parental strain AB1157. Thus, both radiation-resistant and bacteria can repair single-strand breaks in the absence of normal DNA replication. Similar repair was observed in a strain suggesting that DNA polymerase I is not involved. Both radiation-resistant and bacteria also show a small amount of gamma-ray stimulated DNA synthesis under these conditions. It is suggested that neither the gene nor protein synthesis are required for repair of single-strand DNA breaks in the absence of an active DNA replication fork.


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