A half-type ABC transporter TAPL is highly conserved between rodent and man, and the human gene is not responsive to interferon-gamma in contrast to TAP1 and TAP2

TAPL is a half-type ABC transporter with sequence similarity to TAP1 and TA P2 that is transcribed in various rat tissues [Yamaguchi, Y,, Kasano, M., T erada, T., Sate, R., and Maeda, M. (1999) FEES Lett. 457, 231-236]. Primary structures of the human and mouse orthologous counterparts were deduced fr om cDNAs cloned by means of polymerase chain reaction, and they were compar ed with that of the rat. The mammalian TAPLs (rat, mouse, and human) are hi ghly conserved, since about 95% of the amino acid residues are identical be tween rodents and man. Phylogenetic analysis demonstrated that the evolutio nal rate of TAPL is much slower than those of TAP1 and TAPE, although TAPL could have diverged from an ancestor of TAP1 or that of TAP1 and TAP2. The TAPL-GFP fusion protein transiently expressed in Cos-1 cells was co-localiz ed with PDI, suggesting that TAPL is inserted into endoplasmic reticulum me mbrane. The conservation of the peptide-binding motifs of TAP proteins in T APL raises the possibility that the TAPL might be a peptide transporter. Th e gene for human TAPL is assigned to chromosome 12q24.31-q24.32, while thos e for TAP1 and TAP2 are located at the MHC locus of chromosome 6p21.3. Furt hermore, the transcription of TAPL gene is not responsive to interferon-gam ma, in contrast to TAP1 and TAPE. These results indicate that the gene regu lation of TAPL is different from those of TAP1 and TAP2.