NUCLEAR ENCODED GENES REGULATE CHLOROPLAST TRANSLATION

在单细胞绿藻Chlamydomonas rehardtii中发现了一组核编码蛋白，它们与叶绿体编码的PSBA mRNA的5‘-非翻译区(UTR)具有高度的特异性和亲和力。这些蛋白与5‘-UTR的结合是PSBA mRNA翻译所必需的，并通过升高的ADP水平和氧化还原电位来调节，这两个生理事件与光合作用有关。代表其中三个翻译激活子的cDNA已经被分离出来。对其中两个cDNA的序列分析表明，相应的蛋白质代表一个聚A结合蛋白和一个蛋白质二硫键异构酶。此时，第三种蛋白质没有指定的功能。我们已经生产了针对这些蛋白质的抗血清，并分离了两个基因组克隆：对基因组文库的筛选应该可以分离第三个克隆。我们计划对调控每个核编码的PSBA结合蛋白基因的信号转导途径中的主要信号和其他成分进行表征，以了解它们的表达如何影响PSBA mRNA的翻译。这些研究是第一次解决植物中克隆的翻译激活子的特征，并将提供对调节核编码的翻译激活子表达的主要信号的洞察。在酵母中也发现了调节线粒体mRNAs翻译的核编码蛋白，然而，相应的基因还没有被分离出来。因此，这项研究将为揭示核编码的翻译激活子表达的分子机制(S)提供重要的见解，这些信息将适用于那些利用核/细胞器交叉通讯的系统。

A set of nuclear-encoded proteins that bind with high specificity and affinity to the 5'-untranslated region (UTR) of the chloroplast- encoded psbA mRNA have been identified in the unicellular green alga Chlamydomonas reinhardtii. Binding of these proteins to 5'-UTR is required for translation of the psbA mRNA and is regulated through elevated ADP levels and redox potential; two physiological events that are linked to photosynthesis. The cDNAs representing three of these translational activators have been isolated. Sequence analysis of two of the cDNAs has revealed that the corresponding proteins represent a poly A binding protein and a protein disulfide isomerase. A third protein at this time has no assigned function. We have produced antisera against these proteins, and have isolated two of the genomic clones: a screen of a genomic library should allow isolation of the third clone. We plan to characterize the primary signal and other components in the signal transduction pathway that regulate each of the nuclear-encoded psbA binding protein genes in order to understand how their expression influences translation of the psbA mRNA. These studies represent the first to address the characterization of cloned translational activators in plants, and will provide insight into the primary signals that regulate the expression of nuclear-encoded translational activators. Nuclear-encoded proteins that regulate the translation of mitochondrial mRNAs have also been identified in yeast, however, the corresponding genes have not been isolated. Therefore, this research should provide important insight into the molecular mechanism(s) that signal the expression of nuclear-encoded translational activators, information which will be applicable to those systems utilizing nuclear/organelle cross-communication.