Hisayoshi Nozaki1, Hiroyoshi Takano2, Osami Misumi3,4, Kimihiro Terasawa5,6, Motomichi Matsuzaki1, Shinichiro Maruyama1,6, Keiji Nishida3,4, Fumi Yagisawa3,4, Yamato Yoshida7,4, Takayuki Fujiwara3,4, Susumu Takio8, Katsunori Tamura6, Sung Jin Chung2,10, Soichi Nakamura9, Haruko Kuroiwa3,4, Kan Tanaka6, Naoki Sato5 and Tsuneyoshi Kuroiwa3,4
1Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Tokyo, Japan
2Graduate School of Science and Technology, Kumamoto University, Japan
3Department of Life Science, College of Science, Rikkyo (St. Paul’s) University, Tokyo, Japan
4Research Information Center for Extremophile, Rikkyo (St. Paul’s) University, Tokyo, Japan
5Department of Life Sciences, Graduate School of Arts and Sciences, the University of Tokyo, Tokyo, Japan
6Institute of Molecular and Cellular Biosciences, the University of Tokyo, Tokyo, Japan
7Department of Integrated Biosciences, Graduate School of Frontier Sciences, the University of Tokyo, Chiba, Japan
8Center for Marine Environment Studies, Kumamoto University, Kumamoto, Japan
9Laboratory of Cell and Functional Biology, Faculty of Science, University of the Ryukyus, Okinawa, Japan
10Radiation Research Center for Bio-Technology, Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeollabuk-do, Korea
All previously reported eukaryotic nuclear genome sequences have been incomplete, especially in highly repeated units and chromosomal ends. Because repetitive DNA is important for many aspects of biology, complete chromosomal structures are fundamental for understanding eukaryotic cells. Our earlier, nearly complete genome sequence of the hot-spring red alga Cyanidioschyzon merolae revealed several unique features, including just three ribosomal DNA copies, very few introns, and a small total number of genes. However, because the exact structures of certain functionally important repeated elements remained ambiguous, that sequence was not complete. Obviously, those ambiguities needed to be resolved before the unique features of the C. merolae genome could be summarized, and the ambiguities could only be resolved by completing the sequence. Therefore, we aimed to complete all previous gaps and sequence all remaining chromosomal ends, and now report the first nuclear-genome sequence for any eukaryote that is 100% complete.
Our present complete sequence consists of 16546747 nucleotides covering 100% of the 20 linear chromosomes from telomere to telomere, representing the simple and unique chromosomal structures of the eukaryotic cell. We have unambiguously established that the C. merolae genome contains the smallest known histone-gene cluster, a unique telomeric repeat for all chromosomal ends, and an extremely low number of transposons.
By virtue of these attributes and others that we had discovered previously, C. merolae appears to have the simplest nuclear genome of the non-symbiotic eukaryotes. These unusually simple genomic features in the 100% complete genome sequence of C. merolae are extremely useful for further studies of eukaryotic cells.
◊ An open access article from BMC Biology 2007, 5:28 distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), viewed from biologyonline.com.