MESSENGER RNA DECAY OF IMMEDIATE EARLY GENES

在哺乳动物细胞中，c-fos原癌基因是一类 大约50-100个生长因子诱导基因，称为直接 早期基因，其转录本在细胞质中迅速衰减， 半衰期小于30分钟。这类mRNA的不稳定性 区别于大多数哺乳动物的信息， 更稳定，半衰期从几小时到几天不等。 这项建议 专注于阐明哺乳动物中即刻早期基因mRNA降解 细胞，使用c-fos原癌基因作为模型系统。 四个重要的问题得到解决。 第一，功能上 mRNA不稳定性的两个主要c-fos决定因素的重要特征？ 第二，c-fos编码区决定簇的性质是什么？ 不稳定？ 它的不稳定功能是如何与蛋白质结合的 翻译？ 第三，什么是与c- fos不稳定性决定因素 第四，是C- fos mRNA是快速和选择性降解的目标， 其他即刻早期基因mRNA的衰变 审查 c-fos mRNA顺式作用决定簇的结构特征及其性质 c-fos编码区的不稳定性决定因素将涉及创造 人c-fos和兔β-珠蛋白的确定的突变和融合 基因，将这些改变的基因构建体引入小鼠 成纤维细胞，并在体内分析所得mRNA的衰变。 的 细胞质mRNA降解因子鉴定和表征 将涉及在体外系统中重建mRNA衰变， 进行体外mRNA结合测定。 最后，mRNA衰变三 将研究即刻早期基因mRNA以检验其泛化性 c-fos mRNA的衰变机制。 这些研究的结果应该会增强我们对一个基本问题的认识， 基因表达的一个方面，目前还知之甚少。 因为 c-fos原癌基因mRNA的显著不稳定性有助于防止 通过该基因的致癌转化、鉴定和表征 参与c-fos mRNA衰变的细胞因子中， 潜在的定义一类新的癌症的抑制基因。 因此，从拟议研究中学到的知识应 最终将有助于理解 肿瘤发生

In mammalian cells, the c-fos proto-oncogene is a representative of a class of approximately 50-100 growth factor inducible genes, termed immediate early genes, whose transcripts decay rapidly in the cytoplasm with a short half-life of less than 30 min. The instability of this class of mRNA distinguishes it from most mammalian messages, which typically are much more stable with half-lives ranging from hours to days. This proposal focuses on elucidating immediate-early-gene mRNA degradation in mammalian cells, using the c-fos proto-oncogene as a model system. Four important questions are addressed. First, what are the functionally important features of the two major c-fos determinants of mRNA instability? Second, what is the nature of the c-fos coding region determinant of instability? How its destabilizing function is coupled to protein translation? Third, what are the cytoplasmic factors that interact with c- fos instability determinants? Fourth, are the mechanisms by which the c- fos mRNA is targeted for rapid and selective degradation also responsible for the decay of other immediate-early-gene mRNAs? Examination of the structural features of cis-acting determinants of c-fos mRNA and the nature of the c-fos coding region determinant of instability will involve creating defined mutations and fusions of the human c-fos and the rabbit beta-globin genes in vitro, introducing these altered genetic constructs into mouse fibroblasts, and analyzing the decay of the resulting mRNAs in vivo. The identification and characterization of cytoplasmic mRNA degradation factors will involve both reconstituting mRNA decay in an in vitro system and performing in vitro mRNA binding assays. Finally, mRNA decay of three immediate-early-gene mRNAs will be investigated to test for generalization of the decay mechanisms of c-fos mRNA. The results of these studies should enhance our knowledge of a fundamental aspect of gene expression that presently is poorly understood. Because the marked instability of the c-fos proto-oncogene mRNA helps to prevent oncogenic transformation by this gene, identification and characterization of the cellular factors that are involved in the decay of c-fos mRNA has the potential to define a new class of cancer of suppressor genes. Therefore, the knowledge learned form the proposed studies should ultimately be of value to understanding molecular mechanisms of oncogenesis.