Sequence encompassing all of exons 3 through 8 and a portion of exon 9 was replaced with a cassette containing an IRES-lacZ-neo fusion gene. RT-PCR analysis of total embryonic RNA showed an absence of normal transcript in animals possessing a targeted paternal allele and a silenced wild-type maternal allele. Paternal transmission of this allele yielded a lacZ expression pattern similar to that of the endogenous gene. (J:50170)