"The overwhelming majority of chimp proteins about 75% -- are different from ours in at least one amino-acid 'letter," according to Hannon. These amino-acid changes are in most instances slight, but the resulting functional differences the way they affect what proteins do in cells can be great, and presumably help to explain many of our differences from chimpanzees.
Eighty-eight amino-acid differences and what they might signify
Hannon's team applied its focused sequencing method on those areas in the Neandertal sample obtained from Dr. Pbo, and, after several rounds of refinement, they arrived at the number 88: they found only 88 changes in Neandertal protein sequences compared with the modern human. Hannon calls this number "astonishing."
At an early stage of the study, the team identified many more protein differences -- about 1000 -- between modern man and the specific Neandertal individual sampled, a male who died about 49,000 years ago in a cave called El Sidrn, in Spain. But that initial figure was based on comparing the Neandertal sequence to that of the modern human reference genome. When the teams incorporated into their calculations variations in the modern human code that they catalogued in 50 individuals from a range of modern ethnic groups, the number of human-Neandertal protein differences dropped from over 1000 to only 88.
Although Hannon says it will be important to study the functional role of the 88 proteins, he expects that many may prove "neutral," functionally. These would be changes in the genetic code that do not issue in any difference in the function of the associated proteins. If even more human genome samples -- say, from 500 contemporary individuals rather than 50 -- were included in the comparison, the number of differences might drop again, Hannon believes. And if additional Neandertal samples were factored into the comparison, he says,
|Contact: Peter Tarr|
Cold Spring Harbor Laboratory