THE STRUCTURAL BASIS OF MOLECULAR ADAPTATION

The study of molecular adaptation has long been fraught with difficult ies, not the least of which is identifying out of hundreds of amino ac id replacements those few directly responsible for major adaptations. Six studies are used to illustrate how phylogenies, site-directed muta genesis, and a knowledge of protein structure combine to provide much deeper insights into the adaptive process than has hitherto been possi ble. Ancient genes can be reconstructed, and the phenotypes can be com pared to modern proteins. Out of hundreds of amino acid replacements a ccumulated over billions of years those few responsible for discrimina ting between alternative substrates are identified. An amino acid repl acement of modest effect at the molecular level causes a dramatic expa nsion in an ecological niche. These and other topics are creating the emerging field of ''paleomolecular biochemistry.''.