GENOME OF THE RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) ENCODES 2 DISTINCT MUSCLE REGULATORY FACTORS WITH HOMOLOGY TO MYOD

Previously we identified a trout myogenic factor related to MyoD. We n ow present a cDNA encoding a novel trout myogenic factor (TMyoD2) expr essed in embryonic muscle. Nucleotide analysis and amino acid comparis on showed that this cDNA encodes a MyoD-like protein of 275 amino acid s that is distinct but related to TMyoD with 78% identity over the ent ire length. The protein sequence conservation between TMyoD2 and TMyoD was calculated to be 90% within the basic/ helix-loop-helix domain th at is involved in DNA binding and heterooligomerisation. At the nucleo tide level, comparison of TMyoD with TMyoD2 reveals that the translate d regions are flanked by highly divergent 3' and 5' ends. The substant ial differences observed at translated and especially untranslated reg ions strongly suggest that TMyoD and TMyoD2 mRNA originate from differ ent loci. The TMyoD and TMyoD2 mRNA are likely transcribed from two di stinct genes which were duplicated during the tetraploidization of the salmonid genome.