Gain and loss of an intron in a protein-coding gene in Archaea: the case of an archaeal RNA pseudouridine synthase gene.
BACKGROUND
We previously found the first examples of splicing of archaeal pre-mRNAs for homologs of the eukaryotic CBF5 protein (also known as dyskerin in humans) in Aeropyrum pernix, Sulfolobus solfataricus, S. tokodaii, and S. acidocaldarirus, and also showed that crenarchaeal species in orders Desulfurococcales and Sulfolobales, except for Hyperthermus butylicus, Pyrodictium occultum, Pyrolobus fumarii, and Ignicoccus islandicus, contain the (putative) cbf5 intron. However, the exact timing of the intron insertion was not determined and verification of the putative secondary loss of the intron in some lineages was not performed.


RESULTS
In the present study, we determined approximately two-thirds of the entire coding region of crenarchaeal Cbf5 sequences from 43 species. A phylogenetic analysis of our data and information from the available genome sequences suggested that the (putative) cbf5 intron existed in the common ancestor of the orders Desulfurococcales and Sulfolobales and that probably at least two independent lineages in the order Desulfurococcales lost the (putative) intron.


CONCLUSIONS
This finding is the first observation of a lineage-specific loss of a pre-mRNA intron in Archaea. As the insertion or deletion of introns in protein-coding genes in Archaea has not yet been seriously considered, our finding suggests the possible difficulty of accurately and completely predicting protein-coding genes in Archaea.
Yokobori
Shin-ichi
S
Department of Molecular Biology, School of Life Science, Tokyo University of Pharmacy and Life Science, Horinouchi, Hachioji, Tokyo 192-0392, Japan. yokobori@ls.toyaku.ac.jp
Itoh
Takashi
T
Yoshinari
Shigeo
S
Nomura
Norimichi
N
Sako
Yoshihiko
Y
Yamagishi
Akihiko
A
Oshima
Tairo
T
Kita
Kiyoshi
K
Watanabe
Yoh-ichi
Y
D001105:Archaea / Q000201:enzymology / Q000235:genetics*; D019843:Archaeal Proteins / Q000235:genetics; D001483:Base Sequence; D019143:Evolution, Molecular; D019766:Genes, Archaeal; D019751:Intramolecular Transferases / Q000235:genetics*; D007438:Introns; D008969:Molecular Sequence Data; D010802:Phylogeny; D012322:RNA Precursors / Q000235:genetics; D019642:RNA, Archaeal / Q000235:genetics*; D016415:Sequence Alignment; D017423:Sequence Analysis, RNA
D019843:Archaeal Proteins; D012322:RNA Precursors; D019642:RNA, Archaeal; D019751:Intramolecular Transferases; C096995:pseudouridine synthases