Nucleic Acids Research Advance Access originally published online on February 8, 2007
Nucleic Acids Research 2007 35(5):1589-1600; doi:10.1093/nar/gkl1170
Nucleic Acids Research, 2007, Vol. 35, No. 5 1589-1600
© 2007 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.
Nucleic Acid Enzymes |
Homing endonuclease I-TevIII: dimerization as a means to a double-strand break
1Wadsworth Center, New York State Department of Health, Center for Medical Science and 2Department of Biomedical Sciences, School of Public Health, SUNY, 150 New Scotland Avenue, Albany, NY 12208
*To whom correspondence should be addressed. Tel: +518 473 3345; Fax: +518 474 3181; Email: belfort{at}wadsworth.org
Received October 27, 2006. Revised December 20, 2006. Accepted December 21, 2006.
Homing endonucleases are unusual enzymes, capable of recognizing lengthy DNA sequences and cleaving site-specifically within genomes. Many homing endonucleases are encoded within group I introns, and such enzymes promote the mobility reactions of these introns. Phage T4 has three group I introns, within the td, nrdB and nrdD genes. The td and nrdD introns are mobile, whereas the nrdB intron is not. Phage RB3 is a close relative of T4 and has a lengthier nrdB intron. Here, we describe I-TevIII, the H–N–H endonuclease encoded by the RB3 nrdB intron. In contrast to previous reports, we demonstrate that this intron is mobile, and that this mobility is dependent on I-TevIII, which generates 2-nt 3' extensions. The enzyme has a distinct catalytic domain, which contains the H–N–H motif, and DNA-binding domain, which contains two zinc fingers required for interaction with the DNA substrate. Most importantly, I-TevIII, unlike the H–N–H endonucleases described so far, makes a double-strand break on the DNA homing site by acting as a dimer. Through deletion analysis, the dimerization interface was mapped to the DNA-binding domain. The unusual propensity of I-TevIII to dimerize to achieve cleavage of both DNA strands underscores the versatility of the H–N–H enzyme family.