| Budget Amount *help |
¥6,600,000 (Direct Cost: ¥6,600,000)
Fiscal Year 1988: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 1987: ¥5,100,000 (Direct Cost: ¥5,100,000)
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| Research Abstract |
Chloroplast genes are expressed within the prganelles via their own machinery for prttein biogenesis, although the machinery itself is composed not only of their own gene products but also of the nuclear gene products. We have determined the entire DNA sequence of liverwort chloroplast genome and deduced 127 distinct genes. About half of them are concerned with the basic mechanisms of gene expression in the chloroplasts, such as transcription and translation, and share many features with prokaryotic organisms. Chloroplast ribosomes are prokaryotic 70S, and genetic signals such as promotors, terminatews, SD-sequences etc. are also bacteria types. Thus the genetic system of chloroplasts is basically prokaryotic, supporting the hypothesis of endosymbiotic origin of bacteria. On the other hand, however, many chloroplast genes are interruped by introns(catalytic ones of hroup I or II), differring from bacteria, and thus require post-transcriptional RNA splicing for their gene expression. Analysis of chloroplast RNAs prepared from cultured liverwort cells showed that the primary RNA transcripts usually contained poly-cistronic messages which were then processed into smaller mRNAs prior to splicing. If a gene contained two introns, the splicing proceeded successively from the 5' to 3' direction. We also proposed a bimolecular interaction model for trans-splicing. In conclusion, we postulated matulation pathways for mRNAs in chloroplasts from the primary RNA transcripts via RNA processing and splicing cis and trans.
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