Sequence from the within the 3' region of exon 9 to the middle of exon 11 was replaced with a neomycin selection cassette. An absence of transcript was determined by Northern blot analysis of reticulocyte RNA derived from newborns and fetal liver RNA, both obtained from homozygous mutant mice. Western analysis and immunohistochemical analysis showed an absence of the encoded protein in homozygous mutant animals.