著者

武山 尚生 高橋 佑歌 永田 祥平 澤木 佑介 佐藤 友彦 丸山 茂徳 金井 昭夫

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.6, pp.899-912, 2020-12-25 (Released:2021-01-18)

参考文献数

56

被引用文献数

2

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The origin of eukaryotic organisms is one of the most important questions in biology. So far, it has been suggested that eukaryotes are phylogenetically related to Archaea. Indeed, recent progress in archaeal genomic biology seems to have accurately determined the exact position of Archaea in the birth of the Eukaryota. In particular, identifying groups of archaeal species, such as the superphylum TACK and the Asgard archaea, has shown that primitive genes for eukaryotic signature proteins (ESP) already existed in the genomes of these archaeal species. Some ESPs are especially important, including actin and tubulin in the cytoskeleton and the ESCRT complex, which is involved in nuclear membrane formation. There have been many reports that eukaryotic intracellular organelles, such as mitochondria and chloroplasts, evolved from specific symbiotic bacteria. Moreover, eukaryotic genes are disrupted by intronic sequences, which must be removed or “spliced” and the exons connected after the primary transcript is generated, to make a mature functional mRNA. Recently, it has been suggested that the self-splicing factor in both bacterial and archaeal genomes, called “group II intron”, may cause gene disruption. In this review, the frontiers of genome biology are summarized in terms of the importance of prokaryotes (both Archaea and Bacteria) for the origin of Eukarya. From an Earth history perspective, how the increase in atmospheric oxygen concentration at 2.4-2.0 billion years ago may have contributed to the rise of the eukaryotes is discussed.

著者

鶴巻 萌 齋藤 元文 丸山 茂徳 金井 昭夫

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.6, pp.881-898, 2020-12-25 (Released:2021-01-18)

参考文献数

49

被引用文献数

2 5

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It is well known that the evolution of life is affected by environmental factors, and this should be a fundamental perspective when investigating the origin of life; however, this perspective has not been fully addressed in biology. The Hadean Earth had a completely different surface environment from that of today, with no free oxygen, but instead a local environment rich in H2 which was generated by serpentinization, while energy–material circulation was driven by nuclear geysers. It is proposed that an anoxic hot-spring environment, with abundant hydrogen produced by serpentinization, was the birthplace of life. It is also proposed that the Hakuba hot spring in Nagano, Japan, is a Hadean-Earth-like environment with an H2-rich environment. A microbe found there, designated Hakuba OD1, is a member of the Candidate Phyla Radiation (CPR) bacteria group. In this review, CPR bacteria are described and their importance for the origin of life is discussed. The CPR is a bacterial supergroup consisting of dozens of phylum-level lineages of very small bacteria. This group was recently discovered with a metagenomics analysis that allowed unculturable environmental samples to be detected. Biochemical approaches to the CPR bacteria have not yet been successful because almost all the bacteria are unculturable or have not been isolated. However, with the development of massive parallel sequencing technology (next-generation sequencing), the phylogenetic characteristics of the CPR bacteria are becoming clear, and genomic analyses of these bacteria have led to unique discoveries. The sizes of the CPR bacterial genomes range from 400 to 1,500 kilobases (kb), and they contain approximately 400-1,500 genes. Thus, their genomes are remarkably small compared to other well-known and ordinary bacteria, represented by Escherichia coli, which have over 4,000 genes, but are similar to those of symbiotic or parasitic bacteria. The CPR bacterial genomes also lack many of the genes involved in essential metabolic pathways, such as the tricarboxylic acid (TCA) cycle and amino acid biosynthesis, so they seem to obtain their essential metabolites from their environments. It is proposed that this knowledge is important when considering the chemical changes that occurred on primitive Earth, which gave rise to the first forms of life through the processes of chemical evolution. Therefore, it is essential to understand the kinds of protein that are encoded in CPR bacterial genomes when studying the origin of life.

著者

金井 昭夫

出版者

日本ウイルス学会

雑誌

ウイルス (ISSN:00426857)

巻号頁・発行日

vol.61, no.1, pp.25-34, 2011-06-25 (Released:2012-03-20)

参考文献数

48

被引用文献数

2

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真核生物のマイクロRNA (miRNA)にはウイルスゲノムを標的にするものがあり,ウイルスゲノムの中にもmiRNAがコードされるような例が蓄積して来た.これら低分子のRNAはウイルスの感染や増殖に重要な役割を担っている.また,生殖細胞ではpiRNAとよばれる低分子RNAが内在的なトランスポゾンの発現を抑制している.さらに,古細菌や真性細菌ではCRISPR RNAとよばれる低分子RNAがウイルスやファージのゲノムを標的にしていることが明らかになって来た.すなわち,低分子RNAには宿主の生体防御機構と大きく関わっているものがある.低分子RNAを使って,ウイルスやファージばかりでなく,病原性細菌などの増殖をコントロール出来る可能性についても考察する.