AMINO-ACID RACEMIZATION IN AMBER-ENTOMBED INSECTS - IMPLICATIONS FOR DNA PRESERVATION

DNA depurination and amino acid racemization take place at similar rat es in aqueous solution at neutral pH. This relationship suggests that amino acid racemization may be useful in accessing the extent of DNA c hain breakage in ancient biological remains. To test this suggestion, we have investigated the amino acids in insects entombed in fossilized tree resins ranging in age from <100 years to 130 million years. The amino acids present in 40 to 130 million year old amber-entombed insec ts resemble those in a modern fly and are probably the most ancient, u naltered amino acids found so far on Earth. In comparison to other geo chemical environments on the surface of the Earth, the amino acid race mization rate in amber insect inclusions is retarded by a factor of > 10(4). These results suggest that in amber insect inclusions DNA depur ination rates would also likely be retarded in comparison to aqueous s olution measurements, and thus DNA fragments containing many hundreds of base pairs should be preserved. This conclusion is consistent with the reported successful retrieval of DNA sequences from amber-entombed organisms.