THE RHODOPSIN-ENCODING GENE OF BONY FISH LACKS INTRONS

A study of the sequences of the rhodopsin-encoding genes (Rh) in eight fish species from two of the major subdivisions of the teleosts revea ls that no introns are present in the coding region. This contrasts wi th the opsin-encoding genes of all other vertebrates where either four or five introns are invariably found. Phylogenetic analysis shows tha t this intronless teleost Rh is homologous to the intron-containing Rh of amphibia, birds and mammals. Possible mechanisms for intron loss a re discussed, including replacement by homologous conversion of Rh wit h a processed cDNA.