Regulation of Photosynthetic Electron Transport Genes in Chlamydomonas Chloroplasts

[00:91020]大卫·斯特恩叶绿体，光合作用的场所，起源于蓝藻的祖先，并逐渐将其大部分遗传信息转移到细胞核中。因为叶绿体含有多达5000种蛋白质，今天绝大多数都是核起源的。在这些蛋白质中，有无数的蛋白质是正确表达留在叶绿体中的基因所必需的。本项目主要研究绿藻莱茵衣藻（Chlamydomonas reinhardtii）中调节信使RNA寿命的核编码蛋白，以及叶绿体核糖体如何识别蛋白质合成必须启动的位点。该项目将进一步进行早期分析，发现至少有5个核基因编码影响petD mRNA稳定性的产物，该mRNA编码细胞色素b6/f复合物的亚基IV，这是光合作用必需的蛋白质。其中一个基因Mcd1已被克隆，其与petD mRNA相互作用的细节将被阐明。研究人员还将研究另一种基因，其产物可能与Mcd1形成多蛋白复合物的一部分。这个名为mcd4的基因是通过基于光合作用能力的基因筛选确定的。Mcd4已成为研究的目标，因为它似乎与参与叶绿体生物发生的其他核基因具有独特的属性。该项目的第二个方面涉及翻译起始，特别是启动子tRNA与petA翻译起始密码子上游核苷酸之间的相互作用，该密码子编码细胞色素f。将研究这种相互作用的一般情况，以及所谓的shane - dalgarno序列的作用，其在细菌蛋白质合成中的功能是公认的，但其在叶绿体中的作用有些争议和明显可变。总的来说，本项目将阐明真核细胞不同区室之间的通讯机制，这是理解细胞内调节的一个基本问题。

0091020 David SternChloroplasts, the site of photosynthesis, are derived from a cyanobacterial ancestor and have progressively transferred most of their genetic information to the nucleus. Because chloroplasts contain up to 5,000 proteins, today the vast majority are of nuclear origin. Among these proteins are a myriad which are required for correct expression of the genes which remain in the chloroplast. This project focuses on nucleus encoded proteins which regulate messenger RNA lifetime in the green alga Chlamydomonas reinhardtii, as well as on how chloroplast ribosomes recognize the site at which protein synthesis must be initiated. This project will further earlier analyses which revealed that at least 5 nuclear genes encode products which affect the stability of petD mRNA, which encodes subunit IV of the cytochrome b6/f complex, an essential protein for photosynthesis. One of these genes, Mcd1, has been cloned and the details of its interaction with the petD mRNA will be elucidated. Another gene whose product may form part of a multiprotein complex with Mcd1 will also be studied. This gene, mcd4, was identified through a genetic screen based on photosynthetic capability. Mcd4 has been targeted because it appears to have unique attributes with respect to other nuclear genes involved in chloroplast biogenesis. The second aspect of the project concerns translation initiation, and in particular the interaction between the initiator tRNA and the nucleotide upstream of the translation initiation codon of petA, which encodes cytochrome f. The generality of this interaction will be investigated, as well as the role of the so-called Shine-Dalgarno sequence, whose functionality in bacterial protein synthesis is well-established, but whose role in chloroplasts is somewhat controversial and clearly variable. Overall, this project will elucidate mechanisms of communication between different compartments of eukaryotic cells, a fundamental issue in understanding intracellular regulation.