CAP-DEPENDENT AND CAP-INDEPENDENT TRANSLATION BY INTERNAL INITIATION OF MESSENGER-RNAS IN CELL-EXTRACTS PREPARED FROM SACCHAROMYCES-CEREVISIAE
CAP-DEPENDENT AND CAP-INDEPENDENT TRANSLATION BY INTERNAL INITIATION OF MESSENGER-RNAS IN CELL-EXTRACTS PREPARED FROM SACCHAROMYCES-CEREVISIAE
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DOI：
10.1128/mcb.14.11.7322
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发表时间：
1994-11-01
影响因子：
5.3
通讯作者：
SARNOW, P
中科院分区：
文献类型：
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作者：
IIZUKA, N;NAJITA, L;SARNOW, P
从不同的酿酒酵母菌株中制备了翻译提取物。在这些提取物中，5‘端帽结构和3’端poly(A)序列的存在协同促进了mRNA分子的翻译。这些协同效应在其他翻译系统中没有观察到，如兔网织细胞、小麦胚芽和人HeLa细胞制备的翻译系统。由于酵母翻译系统模拟了帽结构和poly(A) tail对体内翻译效率的影响，因此该系统被用于研究病毒和细胞mRNA分子的帽依赖性和帽非依赖性翻译。在酵母提取物的翻译过程中，丙型肝炎病毒和柯萨奇病毒B1的5'非编码区都赋予了一个与帽无关的报告编码区翻译；因此，酵母翻译装置能够启动与帽盖无关的翻译。尽管大多数酵母mrna的翻译是帽依赖性的，但在这些提取物中，编码细胞转录因子TFIID和HAP4的mrna的异常长5'非编码区介导了帽非依赖性翻译。此外，当将TFIID和HAP4 5'非编码区置于双双子mRNA的顺反子间间隔区时，它们都介导了第二个顺反子的翻译，这表明这些先导序列在体外翻译系统中可以通过内部核糖体结合机制启动翻译。这一发现提出了酵母细胞中存在内源性mrna调控翻译的内部翻译起始机制的可能性。
Translation extracts were prepared from various strains of Saccharomyces cerevisiae. The translation of mRNA molecules in these extracts was cooperatively enhanced by the presence of 5'-terminal cap structures and 3'-terminal poly(A) sequences. These cooperative effects could not be observed in other translation systems such as those prepared from rabbit reticulocytes, wheat germ, and human HeLa cells. Because the yeast translation system mimicked the effects of the cap structure and poly(A) tail on translational efficiency seen in vivo, this system was used to study cap-dependent and cap-independent translation of viral and cellular mRNA molecules. Both the 5' noncoding regions of hepatitis C virus and those of coxsackievirus B1 conferred cap-independent translation to a reporter coding region during translation in the yeast extracts; thus, the yeast translational apparatus is capable of initiating cap-independent translation. Although the translation of most yeast mRNAs was cap dependent, the unusually long 5' noncoding regions of mRNAs encoding cellular transcription factors TFIID and HAP4 were shown to mediate cap-independent translation in these extracts. Furthermore, both TFIID and HAP4 5' noncoding regions mediated translation of a second cistron when placed into the intercistronic spacer region of a dicistronic mRNA, indicating that these leader sequences can initiate translation by an internal ribosome binding mechanism in this in vitro translation system. This finding raises the possibility that an internal translation initiation mechanism exists in yeast cells for regulated translation of endogenous mRNAs.