Exon 1, which encodes 96 residues that make up the cytosolic and transmembrane domains as well as a portion of the ectodomain, was deleted by in vitro cre mediated recombination. An aberrant trasncript resulting from a cryptic splice site within intron 1 was detected by RT-PCR. Sequence analysis identified two start codons in intron 1 that are in frame with exon 2. Translation of the aberrant transcript is expected to produce a protein in which the 96 endogenous amino acids are replaced with either 65 or 11 residues encoded by intronic sequence. The novel amino terminal is expected to lack the transmembrane and signal peptide characteristics of the endogenous protein.