Studies on factors involved in post-transcriptional steps in plastids

从烟草叶绿体中分离到5个RNA结合蛋白(RNPs)，并对它们的cDNA和基因进行了分析。所有五个RNP都含有N-末端的一个转运肽、一个酸性结构域和两个朝向C-末端的RNA结合域。它们的基因由四个外显子和三个内含子组成，它们的位置在五个基因中是相同的。这五个RNP虽然对聚(G)和聚(U)有很强的亲和力，但除了成熟的tRNAs外，都能与所研究的所有叶绿体RNA结合，这表明RNA序列特异性很小。通过抗体从叶绿体裂解物中去除所有RNPs后，叶绿体RNA的加工和翻译活性增加。这一结果表明，叶绿体RNPs具有保护和存储RNAs的功能，或者是划分叶绿体转录和翻译系统的功能。

Five RNA-binding proteins (RNPs) have been isolated from tobacco chloroplasts, and their cDNAs and genes were analyzed. All five RNPs contain each a transit-peptide at the N-terminus, an acidic domain, and two RNA-binding domains towards the C-terminus. Their genes consist of four exons and three introns, the position of which is identical among the five genes.All five RNPs, though showing strong affinity to poly (G) and poly (U), bind to all plastid RNAs examined except mature tRNAs, suggesting little RNA sequence specificity. After removing all RNPs by their antibodies from chloroplast lysates, plastid RNA processing and translation activities increased. This result suggests that chloroplast RNPs function to protect and store RNAs, or to partition plastid transcription and translation systems.