Functional Analysis of a novel peptide transporter expressed in brain and testis

TAP样（TAPL）是半型ATP结合盒（ABC）转运蛋白，其与抗原加工相关转运蛋白（TAP）1和TAP 2具有序列相似性，并且在哺乳动物中高度保守[小林，A.，等人（2000）J.Biochem.128，711-718]。采用半定量逆转录聚合酶链反应（RT-PCR）方法研究TAP家族（TAP 1、TAP 2和TAPL）在大鼠体内的组织分布。在年轻雄性大鼠中，在脑和睾丸中检测到较高量的TAPL mRNA，而不是在胸腺和肠中。另一方面，TAP 1和TAP 2 mRNA在胸腺中表达较高。此外，TAP 1在肠组织中的表达水平以及TAP 2在脑和睾丸组织中的表达水平也较高。对大鼠TAPLcDNA序列的分析表明，ATP结合区的羧基端序列是不均一的。至少有四种不同的异构体（C-I，II，III和IV）可以产生的mRNA的选择性剪接，证实了基因组数据搜索。C-III型和C-IV型的羧基端序列均较短，且C-III型的羧基端序列最短。在脑和睾丸中有差异表达。TAPL的羧基末端剪接变体的功能异质性是预期的。

TAP-like (TAPL) is a half type ATP-binding cassette (ABC) transporter with sequence similarity to transporter associated with antigen processing (TAP)1 and TAP2, and is highly conserved in mammals [Kobayashi, A., et al. (2000) J. Biochem. 128, 711-718]. Tissue distribution of TAP family (TAP1, TAP2 and TAPL) in rat was investigated by semi-quantitative Reverse transcriptase polymerase chain reaction (RT-PCR). In young male rat, higher amounts of TAPL mRNA were detected in brain and testis rather than in thymus and intestine. On the other hand, both TAP1 and TAP2 mRNAs were expressed higher in thymus. Furthermore, the expression level of TAP1 in intestine and that of TAP2 in brain and testis were also high. Analysis of rat TAPL cDNAs demonstrated that that the carboxyl terminal sequence of ATP binding region was heterogeneous. At least four different isoforms (C-I, II, III and IV) could be produced by alternative splicing of mRNA, as was confirmed by genomic data search. Both C-III and C-IV types had shorter carboxyl terminal sequences, and the C-III had the shortest. Differential expression of them in brain and testis were observed. The functional heterogeneity of the carboxyl terminal splicing variants of TAPL is expected.