On the origin of the genetic code

The main theories which have been suggested to explain the origin of genetic code organization are discussed. The coevolution theory, which considers the genetic code as a map of the biosynthetic relationships between amino acids, seems to be based on a mechanism that links it closely to certain stages of the origin of metabolism, which makes it preferable to other theories proposed as explanations of genetic code origin. Relationships, incompatibilities and compromises between the various theories are highlighted and these seem to indicate a certain lack of clarity in this field of research. (C) 1997 Academic Press Limited.