Celebrating complementarity.

Abstract

The 1950s witnessed prodigious growth in our knowledge of the chemical nature of the gene, the mechanisms by which the information inherent in its sequence of nucleotide units was conveyed to the cell's machinery for synthesizing proteins, and the mode of operation of that machinery. Watson and Crick raised the curtain by revealing the structure of DNA, notably the complementary pairing of the nucleotides in its twin chains. Identified with the new field of molecular biology, Crick defined and expanded the field of genetic information coding and led attempts to elucidate principles governing information translation into protein. On a parallel and complementary track, biochemists-notably the group led by Paul Zamecnik-were working out the details of the mechanism of protein synthesis: how and where in the cell amino acids were energized, sequenced, and polymerized. These two approaches to closely related problems, separated by a considerable cultural gap, merged dramatically in 1956. Crick's thinking led him to postulate the existence of adaptors -short chains of RNA nucleotide bases that, when linked to amino acids, might make the latter chemically "recognizable" to an RNA template by complementary pairing of their bases with those of the template. Simultaneously, the Zamecnik group discovered enzymes (amino acyl-tRNA synthetases) capable of energizing amino acids and, thence, attaching them to a hitherto unsuspected cellular RNA (transfer RNA). These RNA molecules, in turn, donated their bound amino acids to elongating protein chains on ribosomes, thus appearing to serve the function of adaptors.