8月26日（金）9：00 - 11：00 Room8（70周年記念講堂）
- Reconstructing human history from ancient DNA
(Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen)
Over the past decade, the advent of next-generation DNA sequencing technologies has enabled a revolution in the field of paleogenomics - the study of the genomes of ancient organisms. The reconstruction of the evolutionary history of our own species in particular has been transformed by a wealth of new data, often yielding surprising and unexpected insights into our past.
In this talk I will discuss some of our recent results into human population history through analyses of hundreds of ancient genomes, covering 45,000 years of human evolution from the Upper Paleolithic to the Eurasian Bronze Age.
Allentoft ME, Sikora M, et al. (2015) Population genomics of Bronze Age Eurasia. Nature 522 167-172.
- The Genomic Tag Hypothesis for the Origin of tRNA and Genomic RNA Replication in the RNA World
◯Alan Weiner and Nancy Maizels
(Department of Biochemistry, University of Washington School of Medicine)
Following the discovery of catalytic RNA in 1982 by Tom Cech, Sid Altman, and Norm Pace, most molecular biologists concluded without hesitation that RNA (or something like RNA) was the first "living" molecule on earth. The discovery of catalytic RNA liberated molecular biologists from asking whether DNA (an informational molecule) or protein (a catalytic molecule) came first (the famous "chicken and egg question"). Instead, RNA could be both catalytic and informational, and thus capable of both replication and evolution.
The more we learn about molecular biology and evolution, the more plausible this deceptively simple scenario becomes; however, many difficult problems remain. Two of the most important problems are: How did RNA first arise from prebiotic chemical reactions? And if RNA was the first "living" molecule capable of replication and evolution, how did protein synthesis evolve? In recent breakthroughs, Powner et al. (1) and Becker et al. (2) may have solved the first problem by exploiting the power of what Szostak calls "systems chemistry" (3). We originally addressed the second problem in 1987 with our "Genomic Tag Hypothesis" for the origin of protein synthesis (4) and subsequently extended our model in 1999 (5).
The basic idea of the Genomic Tag Hypothesis is that tRNA first evolved as a 3' terminal structure on linear RNA genomes that enabled the RNA replicase to copy the genomic template from the very 3' end. Thus tRNA would have evolved initially to facilitate replication in the RNA World, and only later have been adapted (or "exapted") as the central component of protein synthesis in the emerging RNP (ribonucleoprotein) World. As evidence for this hypothesis, we describe many "molecular fossils" - RNA viruses, retroplasmids, retroviruses, and modern telomerase that can be arranged in a plausible line of Darwinian "descent with modification." As corollaries, we argue that (a) some RNA viruses are survivors from the RNA World; (b) retroviruses and related pararetroviruses are survivors from a world in transition from RNA to DNA genomes; (c) the CCA-adding enzyme (also known as tRNA nucleotidyltransferase) originally functioned as an RNA telomerase in the RNA World; and (d) modern DNA telomerase activity originated as abortive initiation by a retroelement reverse transcriptase repeatedly copying the 3' end of its genomic RNA.
1. Powner, Gerland, Sutherland (2009) Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions. Nature 459, 239.
2. Becker, Thoma, Deutsch, Gehrke, Mayer, Zipse, Carell (2016) A high-yielding, strictly regioselective prebiotic purine nucleoside formation pathway. Science 352, 833.
3. Szostak (2009) Origins of life: Systems chemistry on early Earth. Nature 459, 171.
4. Weiner and Maizels (1987) 3' terminal tRNA-like structures tag genomic RNA molecules for replication: Implications for the origin of protein synthesis. PNAS 84, 7383
5. Maizels and Weiner (1999) The genomic tag hypothesis: What molecular fossils tell us about the evolution of tRNA. Chapter 3, in The RNA World II, Gesteland, Cech, and Atkins, eds. Cold Spring Harbor Press.
8月26日（金）11：00 - 12：00 Room8（70周年記念講堂）
- Cell wall deficient (L-form) bacteria: from bacterial physiology to the origins of life
Yoshikazu Kawai, Ling Juan Wu, Seoungjun Lee, Katia Mickiewicz and ◯Jeff Errington
(The Centre for Bacterial Cell Biology, Medical School, Newcastle University)
The peptidoglycan cell wall is a defining structure of the bacteria. It is the target for our best antibiotics and fragments of the wall trigger powerful innate immune responses against infection. Surprisingly, many bacteria can switch almost effortlessly into a cell wall deficient “L-form” state. These cells become completely resistant to many antibiotics and may be able to pass under the radar screen of our immune systems. Studies of L-forms have provided surprising insights into various aspects of bacterial cell physiology and biochemistry, as well as providing a model illuminating how the earliest true cells on the planet might have proliferated. Recent studies have revealed that rapid growth of L-forms, as well as accurate chromosome segregation and assembly of components of the division machinery, can occur in the absence of a cell wall, provided that the L-forms are artificially constrained into a cylindrical shape of appropriate dimensions.
Leaver et al. 2009 (Nature 457, 849-853); Mercier et al. 2013 (Cell 152, 997-1007); Errington 2013 (Open Biology 3, 120143); Mercier et al. 2014 (eLife 04629); Kawai et al. 2015 (Current Biology 25, 1613-1618); Mercier et al. 2016 (Nature Microbiology 1, 16091).