An 18 kb segment containing 10.5 kb of 5'- and 1 kb of 3'-regulatory sequence was isolated from a BALB/c cosmid library. The myc epitope was introduced by site-directed mutagenesis after serine at the second amino acid position.An additional mutation was introduced by site-directed mutagenesis that resulted in an arginine to cytosine change at amino acid residue 113. The transgenic mouse line was generated from a founder animal expressing the mutant at sub-stoichiometric level (<=30%) compared with the endogenous gene. (J:145782, J:153496)