The coding region was disrupted by a hygromycin selection cassette inserted by homologous recombination. This construct was used to transfect mice in which the Art2atm1Fkn allele had already been created Transcript was undetected in homozygous mutant mice by RT-PCR analysis of T cells isolated from lymph nodes. FACS analysis of thymocytes and lymphocytes indicated a lack of protein expression on the cell surface.