Regulation of Photosynthetic Electron Transport Genes in Chlamydomonas Chloroplasts

0091020大卫末端叶绿体，光合作用的场所，来自蓝藻的祖先，并逐渐将它们的大部分遗传信息转移到细胞核。因为叶绿体含有多达5,000种蛋白质，所以今天绝大多数蛋白质都来自于核。在这些蛋白质中，有无数种蛋白质是正确表达留在叶绿体中的基因所必需的。该项目的重点是调节绿藻衣藻中信使RNA寿命的核编码蛋白质，以及叶绿体核糖体如何识别蛋白质合成必须启动的位置。该项目将在更早的时候进一步分析，发现至少5个核基因编码影响PETD mRNA稳定性的产物，PETD mRNA编码细胞色素b6/f复合体的亚基IV，细胞色素b6/f复合体是光合作用所必需的蛋白质。其中一个基因Mcd1已经被克隆，它与PETD mRNA相互作用的细节将被阐明。另一个基因也将被研究，该基因的产物可能形成与Mcd1的多蛋白复合体的一部分。这个基因mcd4是通过基于光合作用能力的遗传筛选而鉴定出来的。Mcd4之所以成为靶标，是因为它似乎与参与叶绿体生物发生的其他核基因相比具有独特的属性。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的核苷酸之间的相互作用，该起始密码子编码细胞色素f。这种相互作用的一般性将被研究，以及所谓的Shine-Dalgarno序列的作用，它在细菌蛋白质合成中的功能是众所周知的，但它在叶绿体中的作用存在一定的争议和明显的变异性。总体而言，该项目将阐明真核细胞不同隔室之间的通信机制，这是理解细胞内调节的基本问题。

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.