The use of protein characteristics to assess the retrievability of ancient DNA from ancient bones

The ability to retrieve DNA from ancient specimens has been one of the greatest achievements of the past decade, and has opened a totally new field of research with applications in seemingly distant domains such as archeobotany, the molecular phylogeny of extinct genomes, human paleopathology and the genetic of ancient human populations. However, extraction of ancient DNA has often a very low rate of success, prompting researchers to develop screening methods for the selection of promising specimens. With this goal in mind, we studied the amino acid content of nine human bones of ancient origin. We demonstrate that a single HPLC chromatogram is indicative of the integrity of ancient bone proteins. Among five specimens containing amplifiable DNA, four exhibited a protein content similar to that of contemporary bone protein content. Three of the four specimens, from which we were unable to extract any amplifiable DNA, had an amino acid content strikingly different from that of contem-porary bone. A non-parametric statistical test, Kendall's tau, was used to show that protein content and PCR products, are probably correlated (at a 95% confidence level). In addition, the D/L Asp and D/L Glu racemization ratios obtained are indicative of the presence of ancient organic compounds. We propose that protein analysis should be systematically performed in studies where there are many samples in order to select the specimens that are most likely to contain retrievable ancient DNA.