A flexible genetic code, or why does selenocysteine have no unique codon?

Recent studies have revealed that the modified amino acid selenocysteine is directly incorporated into a polypeptide chain by the translation of a UGA codon, probably through the action of a minor species of tRNA_UGA^Ser acting as a natural UGA suppressor. A mechanism using a termination codon as the codon for a modified amino acid would provoke several intriguing questions. These could all be unilaterally answered by a new vision of the genetic code, flexible in character, and influenced in its expression by the physiology of the cell.