Part of exon 3 and exons 4-9 were replaced by a neomycin cassette via homologous recombination. These exons contained sequence coding for the entire Ba fragment and a large part of the first serine protease domain. Transcripts from homozygous mutant liver were shorter than that of wild-type mice, putatively the truncated, non-functional transcript from the mutant allele. (J:47578)