The kkt mutant mouse was produced by the random insertion of a fusion transgene in which the myogenin promoter was used to direct expression of a human myf5 cDNA-IRESLacZ bicistronic transcript. Heterozygous animals contain about 15 copies of the transgene as determined by Southern blot analysis. Southern blot analysis suggested that a small deletion of less than 10 kb exists at the transgene integration site. (J:60410)