Ye X, Fong P, Iizuka N, Choate D, Cavener D R
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
Mol Cell Biol. 1997 Mar;17(3):1714-21. doi: 10.1128/MCB.17.3.1714.
The 5' untranslated regions (UTRs) of the Drosophila Ubx and Antp genes were tested for their ability to promote cap-independent translation initiation. The Ubx and the Antp 5' UTR were inserted between the CAT and lacZ coding sequences in a dicistronic gene and tested for IRES activity in transgenic Drosophila. Northern analysis of the mRNAs showed the presence of the predicted full-length dicistronic mRNAs. High CAT activity was expressed from the first cistron from all of the dicistronic constructs introduced into the fly genome. The dicistronic transgenic strains bearing the Ubx and Antp IRES elements expressed significant levels of beta-galactosidase (betaGAL) from the second cistron whereas little or no betaGAL was expressed in the controls lacking the IRESs. In situ analysis of betaGAL expression in the transgenic strains indicates that expression of the second cistron is spatially and temporally regulated. Although the developmental patterns of expression directed by the Antp and Ubx IRESs overlap, they exhibit several differences indicating that these IRESs are not functionally equivalent.
对果蝇Ubx和Antp基因的5'非翻译区（UTR）促进不依赖帽结构的翻译起始的能力进行了测试。将Ubx和Antp的5'UTR插入到双顺反子基因的CAT和lacZ编码序列之间，并在转基因果蝇中测试其内部核糖体进入位点（IRES）活性。对mRNA的Northern分析显示存在预测的全长双顺反子mRNA。从导入果蝇基因组的所有双顺反子构建体的第一个顺反子中都表达出了高CAT活性。携带Ubx和Antp IRES元件的双顺反子转基因品系从第二个顺反子中表达出了显著水平的β-半乳糖苷酶（βGAL），而在缺乏IRES的对照中几乎没有或没有表达βGAL。对转基因品系中βGAL表达的原位分析表明，第二个顺反子的表达在空间和时间上受到调控。尽管由Antp和Ubx IRES指导的表达发育模式有重叠，但它们表现出一些差异，表明这些IRES在功能上并不等同。
