A 2314 bp segment encoding Nprl3 promoter P6 (Rr246493) and exon 1 was replaced with a loxP site flanked neomycin resistance gene cassette. Subsequent cre-mediated recombination removed the neo cassette. RNA-FISH analysis indicates Nprl3 expression is eliminated in many tissues but not in erythroid cells. Expression in erythroid cells from homozygous mice is about 50% that of wild-type, presumably from alternatively spliced transcripts with alternative 1st exons. (J:184965)