vi The word ppotein, coined one and a half century ago from the 1TpOTE:toa ("proteios" = of primary importance), underlines the "primary importance" ascribed to proteins from the time they were described as biochemical entities. But the unmatched compl~xity of the process involved in their biosynthesis was (understandably) overlooked. Indeed, protein biosynthesis was supposed to be nothing more than the reverse of protein degradation, and the same enzymes known to split a protein into its constituent amino acids were thought to be able, under adequate conditions, to reconstitute the peptide bond. This oversimplified view persisted for more than 50 years: It was just in 1940 that Borsook and Dubnoff examined the thermodynamical aspects of the process, and concluded that protein synthesis could not be the reverse of protein degradation, such an "uphill task being thermody­ namically impossible ... . " The next quarter of a century witnessed the unravelling of the basic mechanisms of protein biosynthesis, a predictable aftermath of the Copernican revolution in biology which followed such dramatic de­ velopments as the discovery of the nature of the genetic material, the double helical structure· of DNA, and the determination of the ge­ netic code. Our present understanding of the sophisticated mechan­ isms of regulation and control is a relatively novel acquisition, and recent studies have shed some light into the structure and organi­ zation of the eukaryotic gene.