A 100%-complete sequence reveals unusually simple genomic features in the hot-spring red alga Cyanidioschyzon merolae.
BACKGROUND
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.


RESULTS
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.


CONCLUSIONS
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.
Nozaki
Hisayoshi
H
Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Tokyo, Japan. nozaki@biol.s.u-tokyo.ac.jp
Takano
Hiroyoshi
H
Misumi
Osami
O
Terasawa
Kimihiro
K
Matsuzaki
Motomichi
M
Maruyama
Shinichiro
S
Nishida
Keiji
K
Yagisawa
Fumi
F
Yoshida
Yamato
Y
Fujiwara
Takayuki
T
Takio
Susumu
S
Tamura
Katsunori
K
Chung
Sung Jin
SJ
Nakamura
Soichi
S
Kuroiwa
Haruko
H
Tanaka
Kan
K
Sato
Naoki
N
Kuroiwa
Tsuneyoshi
T
D001483:Base Sequence; D002874:Chromosome Mapping; D004251:DNA Transposable Elements / Q000235:genetics; D048028:DNA, Algal / Q000737:chemistry / Q000235:genetics*; D005057:Eukaryotic Cells / Q000378:metabolism; D016678:Genome; D023281:Genomics / Q000379:methods; D006657:Histones / Q000235:genetics; D045482:Hot Springs / Q000382:microbiology*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D005810:Multigene Family; D000461:Rhodophyta / Q000235:genetics*; D017422:Sequence Analysis, DNA; D016615:Telomere / Q000235:genetics
D004251:DNA Transposable Elements; D048028:DNA, Algal; D006657:Histones