The floxed region encompassing about 10 kb of sequence, including a neo cassette and exons 3 and 4, was excised via cre mediated recombination in the germline. The deletion eliminated sequence encoding amino acids 10 through 87 and resulted in a frameshift mutation after codon 9. Western blot analysis indicated an absence of protein in thymocytes and CD3+ T cells. Sequence and splice sites corresponding to the testis-expressed isoform were left intact.