An insertion-type vector was used to create mutations in exon 26 at codon 1785 to alter this residue from an asparagine to a stop codon (N1785X). Western blot analysis on plasma derived from heterozygous and homozygous mice demostrated that a mutant, truncated protein is expressed from this allele, and the expression of the ApoB48 and ApoB100 isoforms was abolished. (J:51549)