Nucleic acids

Few recent advances have, for better or for worse, had such an impact on biological thinking as the discovery of base-pairing in nucleic acids. These complementariness principles do not only underlie current ideas on the structure of the nucleic acids, but they form the foundation of all speculations, more or less well- founded, on their physical properties (denaturation, hypochromic- ity, etc.), on the transfer of biological information from deoxy- ribonucleic acid to ribonucleic acid, and on the role of the latter in directing the synthesis of specific proteins. They form the basis of present explanations of the manner in which the amino acids are activated before being assembled to make a protein; they are being invoked incessantly in attempts to unravel the nucleotide code which is thought to be responsible for specifying the amino acid sequence of proteins.

It will, perhaps, surprise many readers, into whose ears a different version has been drummed for years, to learn that the first announcement of base-pairing in nucleic acids was made in an article, published early in 1950, which forms Chapter 1 of this book; the statement itself will be found on page 13. Those to whom it may sound unusually modest or restrained are asked to consider that at that time the new science of molecular biology did not yet exist.

should like to use this occasion to thank the several publishers for the permission to reprint these articles.

The last two chapters, Nos. 10 and 11, have not been pubHshed before and are of an entirely different kind, stepping forth, as they do, without the stately periwig of a list of references. They should be considered as a divertimento, though not without pas- sages in a minor key; specimens of a sort that rarely finds its way into a book dealing with scientific matters. Chapter 10 is a specimen of a recent lecture, as it was prepared for actual delivery, without undergoing the