Lack of SOS repair in Streptococcus pneumoniae. 
Wild-type strains of Streptococcus pneumoniae were non-mutable by UV radiation and thymidine starvation.  Moreover, UV-irradiated pneumococcal omega 2 phages were not reactivated in an irradiated host.  This suggests that, in pneumoococcus, there is no efficient inducible repair process similar to the SOS repair described in detail for E. coli.  We also report that mutations cannot be induced by a process thought to be linked to competence during transformation with isogenic wild-type DNA either on wild-type strains or in strains in which the hex function of excision and repair of mismatched bases is inactive.