The pGT0TMpfs gene trap, containing CD4 transmembrane domain/beta-galactosidase, neomycin phosphotransferase reporter fusion protein (beta-geo), inserted in intron 13. This truncates the coding region of the gene before exon 14 at codon 459 (versus 1551 wild-type). The catalytic domain is encoded by exons 34-41 so this yields a null allele. Immunoblots confirm that no peptide is produced from this allele.