Identity determinants of Escherichia coli tRNA^Tyr were examined using in vitro transcripts. The first and second anticodon nucleotides were base-specifically involved in tRNA recognition of tyrosyl-tRNA synthetase, whereas the third anticodon nucleotide was not. None of the identity determinants were found in the acceptor stem, except the discriminator base A73. With respect to the long variable arm, a stem of three base pairs in length was required for tyrosylation, while the sequence of the arm was not essential. From the results of identity conversion experiments, the discrimination modes of tRNA^Tyr from other amino acid specific tRNAs sharing some of the identity determinants of tRNA^Tyr were discussed.

In the session of “Mars and Titan”, recent results of both experimental and theoretical research were presented along with exploration data from both the Mars Exploration Rovers (MER) and the Cassini mission. Mars may have had a warm and wet climate during the late-stage heavy bombardment period and nurtured life. Titan has an extremely reducing atmosphere, in which complex abiotic organic chemistry taking place. Studying these planets will help us understand the nature of origin of life on Earth.

The symposium “Coevolution of earth and life” held in 30^th SSOEL-Japan meeting- ISOLAB’05 is reported. In the symposium, keynote lecture was provided by Prof. J. L. Kirschvink, who reported on the Paleoproterozoic snowball earth hypothesis. He explained the possibility that the climate disaster is triggered by the evolution of oxygenic photosynthesis. Prof. A. Yamagishi reported his recent experimental results of the last common ancestor of all the living organisms, which he named Commonote. His experimental results supported the hypothesis that the common ancestor was hyperthermophilic. Prof. S. Itoh reported the significance of the photosynthesis on the early evolution of life and earth. He proposed that the photosynthetic system has much more variation than recognized earlier. Prof. T. Hashimoto reported on his resent results of the analysis of 22 genes of eukaryotic species. He emphasized that the deep branching of three amitochondriate lineages, Microsporidia, Diplomonadida and Parabasalia are caused by the long-branch attraction, and is misleading. Prof. Y. Isozaki reported the mass extinction events in the Paleozoic. He explained the possible relation of mantle plume and Paleozoic-Mesozoic extinction. These reports illuminated the ever-increasing knowledge in each of earth science and life science, though there are still many unsettled controversial issues. However, every audience have noticed that these two fields of science can’t proceed ignoring the other and that the clearer picture of early history of earth and life is now emerging by the concomitant progress of the two sciences.

Since 1995, more than 160 extrasolar planets have been discovered. The recent rapid development of extrasolar planets allows us to expect existence of Earth-like planets in extrasolar planetary systems. In this session, present status and future perspective of observation of extrasolar planets and development of planet formation theory are reviewed. In particular, extrasolar terrestrial planets and possibility of extrasolar life are focused. More than 10 percent of solar type stars in our galaxy may harbor Earth-like planets having ocean on their surface. Near future space telescopes will try to detect bio-markers, such as ozone, in the planetary atmosphere.