Nucleic Acids Research Advance Access originally published online on October 19, 2006
Nucleic Acids Research 2006 34(20):5778-5789; doi:10.1093/nar/gkl699
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Nucleic Acids Research, 2006, Vol. 34, No. 20 5778-5789
© 2006 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
The germ line limited M element of Tetrahymena is targeted for elimination from the somatic genome by a homology-dependent mechanism
Biology Department, Washington University St. Louis, MO 63130, USA
*To whom correspondence should be addressed. Tel: +1 314 935 8838; Fax: +1 314 935 4432; E-mail: dchalker{at}biology2.wustl.edu
Received May 5, 2006. Revised September 1, 2006. Accepted September 5, 2006.
A RNA interference (RNAi) like mechanism is involved in elimination of thousands of DNA segments from the developing somatic macronucleus of Tetrahymena, yet how specific internal eliminated sequences (IESs) are recognized remains to be fully elucidated. To define requirements for DNA rearrangement, we performed mutagenesis of the M element, a well-studied IES. While sequences within the macronucleus-retained DNA are known to determine the excision boundaries, we show that sequences internal to these boundaries are required to promote this IES's rearrangement. However, this element does not contain any specific sequence required in cis as removal of its entire left or right side was insufficient to abolish all rearrangement. Instead, rearrangement efficiency correlated with the overall size of the M element sequence within a given construct, with a lower limit of nearly 300 bp. Also, the observed minimal region necessary to epigenetically block excision supports this size limit. Truncated M element constructs that exhibited impaired rearrangement still showed full transcriptional activity, which suggests that their defect was due to inefficient recognition. This study indicates that IESs are targeted for elimination upon their recognition by homologous small RNAs and further supports the idea that DNA elimination is a RNAi-related mechanism involved in genome surveillance.
Present addresses: Christina A. Kowalczyk, Department of Cell and Molecular Biology, Northwestern University, Chicago, IL 60611, USA
Alissa M. Anderson, Program of Molecular Biosciences, University of Chicago, Chicago, IL 60637, USA
Maria Arce-Larreta, University of Utah Medical School, Salt Lake City, UT 84132, USA
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