A 1000 kb YAC transgene (788H12) containing the entire human presenilin-1 gene was altered to include the Familial Alzheimer's Disease- (FAD-) associated histidine-to-arginine substitution at amino acid position 163 (H163R). The transgene also includes approximately 550 kb of upstream and 350 kb of downstream flanking DNA. Semi-quantitative RT-PCR of multiple tissues shows expression of H163R mutant human mRNA at 50-70% of the level of wild-type mouse transcripts. Transgenic tissues express a wide spectrum of human presenilin-1 mRNA and protein species; alternatively spliced human mRNAs encoding presenilin 1, with or without the tetrapeptide VRSQ, are detected, and western blot analysis reveals accumulation of an 18-kDa C-terminal peptide.