Sepulveda A R, Carter B Z, Habib G M, Lebovitz R M, Lieberman M W
Department of Pathology, Baylor College of Medicine, Houston, Texas 77030.
J Biol Chem. 1994 Apr 8;269(14):10699-705.
The mouse gamma-glutamyl transpeptidase (gamma GT) gene encodes six distinct mRNAs that differ in their 5'-untranslated regions but appear to code for the same protein. To elucidate the mechanisms that generate these different mRNAs we determined the transcription start sites of gamma GT kidney mRNAs and investigated the ability of the 5'-flanking regions of mRNAs I, II, IV, V, and VI to direct transcription of chloramphenicol acetyltransferase (CAT) reporter gene constructs in a mouse kidney cell line. Types I, II, and VI mRNAs show heterogeneous start sites, whereas types IV and V have more precise initiation sites. Only the type V 5'-flanking region contains a TATA-like element. The highest CAT activities were observed with 416 base pairs of type II and 240 base pairs of type IV flanking regions. We have also shown that types II and IV represent the predominant gamma GT mRNAs in kidney; therefore, these CAT activities correlate well with the relative amount of each gamma GT mRNA. This study shows that the mouse gamma GT gene is transcribed from at least five and possibly six different promoters. In addition, the gamma GT promoters show cell specificity because no significant CAT activity was detected when these constructs were introduced into NIH-3T3 fibroblasts.
小鼠γ-谷氨酰转肽酶（γGT）基因编码六种不同的mRNA，它们的5'-非翻译区不同，但似乎编码相同的蛋白质。为了阐明产生这些不同mRNA的机制，我们确定了γGT肾mRNA的转录起始位点，并研究了mRNA I、II、IV、V和VI的5'-侧翼区在小鼠肾细胞系中指导氯霉素乙酰转移酶（CAT）报告基因构建体转录的能力。I型、II型和VI型mRNA显示出异质性起始位点，而IV型和V型具有更精确的起始位点。只有V型5'-侧翼区含有类似TATA的元件。用416个碱基对的II型和240个碱基对的IV型侧翼区观察到最高的CAT活性。我们还表明，II型和IV型代表肾中主要的γGT mRNA；因此，这些CAT活性与每种γGT mRNA的相对量密切相关。这项研究表明，小鼠γGT基因至少从五个可能六个不同的启动子转录。此外，γGT启动子显示出细胞特异性，因为当将这些构建体导入NIH-3T3成纤维细胞时未检测到明显的CAT活性。
