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4. Paabo S. et al.. J. Biol. Chem. 264 9709 (1989)]. Studies of ancient human remains provide information on long-term rates of DNA decay and/or modification and thus a highly conservative estimate of minimum DNA amounts required for prolonged storage under more ideal conditions. About 0.1% of the DNA extracted from ancient decomposed tissue is unmodified [(1);
5. Handt O., et al.., Am. J. Hum. Genet. 59, 368 (1996)]. However, as little as 100 to 300 femtograms of this unmodified DNA can serve as a PCR template (2). In the prototype we have executed, information is stored in 20 nanograms (20,000 picograms) of identical DNA molecules ∼250 base pairs in size [see text and (8)], far above the 100-picograms range. Moreover, use of this large number of molecules (about 80 billion) as PCR templates in our readout procedure should greatly suppress effects of any base modifications during prolonged storage that yield sequence changes in individual DNA molecules