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

TAP-like(TAPL)是一种半型三磷酸腺苷结合盒(ABC)转运蛋白，与抗原处理相关转运蛋白(TAP)1和TAP2序列相似，在哺乳动物中高度保守[Kobayashi，A.，et al.(2000)J.Biochem。128,711-718]。用半定量逆转录聚合酶链式反应(RT-PCR)研究TAP家族(TAP1、TAP2和TAPL)在大鼠体内的组织分布。在幼年雄性大鼠中，TAPL mRNA在脑和睾丸中的表达较高，而在胸腺和肠道中的表达较少。另一方面，TAP1和TAP2mRNAs在胸腺中的表达水平较高。此外，TAP1在肠道中的表达水平较高，TAP2在脑和睾丸中的表达水平也较高。对大鼠TAPL基因的分析表明，三磷酸腺苷结合区的羧基末端序列是异质性的。基因组数据搜索证实，至少有四种不同的亚型(C-I、II、III和IV)可以通过mRNA的选择性剪接产生。C-III和C-IV都有较短的羧基末端序列，C-III最短。观察它们在脑和睾丸中的差异表达。TAPL的羧基末端剪接变异体的功能异质性是可以预料的。

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.