The floxed neomycin selection cassette that replaced all of exons 2 and 3 and a portion of exon 4 in Mbl1tm1Mnz was excised from the germline via cre mediated recombination. Normal transcript was undetected by Northern blot analysis of total RNA obtained from thioglycolate-stimulated livers of homozygous mutant mice. (J:84540)