This Article Full Text Full Text (PDF) Other Versions of this Article: EC.00192-07v1 6/10/1795    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Howard-Till, R. A. Articles by Yao, M.-C. Search for Related Content PubMed PubMed Citation Articles by Howard-Till, R. A. Articles by Yao, M.-C.

Tudor Nuclease Genes and Programmed DNA Rearrangements in Tetrahymena thermophila

Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109,¹ Molecular and Cellular Biology Program, University of Washington, Seattle, Washington 98195,² Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529³

Received 27 May 2007/ Accepted 3 August 2007

Proteins containing a Tudor domain and domains homologous to staphylococcal nucleases are found in a number of eukaryotes. These "Tudor nucleases" have been found to be associated with the RNA-induced silencing complex (A. A. Caudy, R. F. Ketting, S. M. Hammond, A. M. Denli, A. M. Bathoorn, B. B. Tops, J. M. Silva, M. M. Myers, G. J. Hannon, and R. H. Plasterk, Nature 425:411-414, 2003). We have identified two Tudor nuclease gene homologs, TTN1 and TTN2, in the ciliate Tetrahymena thermophila, which has two distinct small-RNA pathways. Characterization of single and double KOs of TTN1 and TTN2 shows that neither of these genes is essential for growth or sexual reproduction. Progeny of TTN2 KOs and double knockouts occasionally show minor defects in the small-RNA-guided process of DNA deletion but appear to be normal in hairpin RNA-induced gene silencing, suggesting that Tudor nucleases play only a minor role in RNA interference in Tetrahymena. Previous studies of Tetrahymena have shown that inserted copies of the neo gene from Escherichia coli are often deleted from the developing macronucleus during sexual reproduction (Y. Liu, X. Song, M. A. Gorovsky, and K. M. Karrer, Eukaryot. Cell 4:421-431, 2005; M. C. Yao, P. Fuller, and X. Xi, Science 300:1581-1584, 2003). This transgene deletion phenomenon is hypothesized to be a form of genome defense. Analysis of the Tudor nuclease mutants revealed exceptionally high rates of deletion of the neo transgene at the TTN2 locus but no deletion at the TTN1 locus. When present in the same genome, however, the neo gene is deleted at high rates even at the TTN1 locus, further supporting a role for trans-acting RNA in this process. This deletion is not affected by the presence of the same sequence in the macronucleus, thus providing a counterargument for the role of the macronuclear genome in specifying all sequences for deletion.

Published ahead of print on 22 August 2007.

This article has been cited by other articles:

• Li, C.-L., Yang, W.-Z., Chen, Y.-P., Yuan, H. S. (2008). Structural and functional insights into human Tudor-SN, a key component linking RNA interference and editing. Nucleic Acids Res 36: 3579-3589 [Abstract] [Full Text]