The carboxyl terminal sequence of rat transporter associated with antigen processing (TAP)-like (ABCB9) is heterogeneous due to splicing of its mRNA.

Transporter associated with antigen processing (TAP)-like (TAPL) is a half-type ATP-binding cassette (ABC) transporter with sequence similarity to TAP1 and TAP2 and is highly conserved in mammals. Tissue distribution of the TAP family (TAP1, TAP2, TAPL) in rat was investigated using the semi quantitative reverse-transcriptase polymerase chain reaction (RT-PCR). In young male rat, greater amounts of TAPL mRNA were detected in the brain and testis than in the thymus and intestine. On the other hand, both TAP1 and TAP2 mRNAs had higher expression in the thymus. Furthermore, the expression level of TAP1 in the intestine and that of TAP2 in the brain and testis were also high. Analysis of rat TAPL cDNAs demonstrated that the carboxyl terminal sequence of the ATP-binding region was heterogeneous. At least four different isoforms (C-I, -II, -III, -IV) could be produced by alternative splicing of mRNA, as was confirmed by a genomic data search. Both C-III and C-IV types had shorter carboxyl-terminal sequences, and the C-III had the shortest sequence. The functional heterogeneity of the carboxyl-terminal splicing variants of TAPL is discussed.