A 3' portion of exon 1 (194 nt) was replaced along with approximately 800 nt of intron 1 by a cassette containing Beta-gal followed by floxed neo. The deleted sequence encoded the putative signal peptide, from the start codon to the first leucine-rich repeat. Endogenous transcript was undetected in homozygous mutant mice by RNase protection. The expression pattern of Beta-gal was similar to that of the endogenous gene. (J:83292)