Dipicolinic Acid Greatly Enhances Production of Spore Photoproduct in Bacterial Spores upon UV Irradiation.

Formation of the spore photoproduct (SP) (5-thyminyl-5,6-dihydrothymine) in DNA of dormant spores of Bacillus subtilis upon UV irradiation is due to binding of alpha/beta-type small, acid-soluble proteins (SASP). However, the yield of SP as a function of UV fluence is approximately 15-fold higher in spores than in an alpha/beta-type-SASP-DNA complex in vitro. The yield of SP as a function of UV fluence in forespore DNA from mutants which make alpha/beta-type SASP but not dipicolinic acid (DPA) was 10 to 20 times lower than that in dormant spores. Furthermore, the yield of SP as a function of UV fluence in an alpha/beta-type-SASP-DNA complex in vitro was increased sixfold by DPA. These data provide further support for the idea that the high DPA level in dormant spores increases the yield of SP as a function of UV fluence and thereby sensitizes spores to UV.