ENDOGENOUS DNA MODIFICATIONS IN AQUATIC ORGANISMS AND THEIR PROBABLE BIOLOGICAL SIGNIFICANCE

1. Novel DNA modifications were detected in the aquatic organisms belonging to the phyla Porifera, Arthropoda, Echinodermata, Protochordata and Pisces by a generally applicable P-32-post-labeling technique. 2. These modifications are lipophilic and different to 5-methylcytosine. They are unrelated to trace RNA contamination. 3. Up to 5-fold interorganism and 1100-fold interspecies variations were observed in the level of modifications, the highest being in P. lividus (Echinodermata), and lowest in C. carpio (Pisces). 4. All the animals showed maximum levels in the months of March and April which coincided with their reproductive phase. In the subsequent months modifications were either undetectable or only slightly present. 5. The fact that modifications were induced in the absence of any known exogenous factors suggests the involvement of some endogenous mechanism for their origin which may contribute to important biologic consequences.