Abstract
Mammalian telomeres are specialized chromatin structures that require the telomere binding protein, TRF2, for maintaining chromosome stability. In addition to its ability to modulate DNA repair activities, TRF2 also has direct effects on DNA structure and topology. Given that mammalian telomeric chromatin includes nucleosomes, we investigated the effect of this protein on chromatin structure. TRF2 bound to reconstituted telomeric nucleosomal fibers through both its basic N-terminus and its C-terminal DNA binding domain. Analytical agarose gel electrophoresis (AAGE) studies showed that TRF2 promoted the folding of nucleosomal arrays into more compact structures by neutralizing negative surface charge. A construct containing the N-terminal and TRFH domains together altered the charge and radius of nucleosomal arrays similarly to full-length TRF2 suggesting that TRF2-driven changes in global chromatin structure were largely due to these regions. However, the most compact chromatin structures were induced by the isolated basic N-terminal region, as judged by both AAGE and atomic force microscopy. Although the N-terminal region condensed nucleosomal array fibers, the TRFH domain, known to alter DNA topology, was required for stimulation of a strand invasion-like reaction with nucleosomal arrays. Optimal strand invasion also required the C-terminal DNA binding domain. Furthermore, the reaction was not stimulated on linear histone-free DNA. Our data suggest that nucleosomal chromatin has the ability to facilitate this activity of TRF2 which is thought to be involved in stabilizing looped telomere structures.
Highlights
The eukaryotic genome is packaged into complex nucleoprotein structures known as chromatin
To better understand how TRF2 performs this function in the context of chromatin, we analyzed the binding of TRF2 to fibers of nucleosomal arrays in comparison to histone-free DNA
DNA and nucleosomal arrays were sedimented with similar concentrations of TRF2B (EC50 = 10–12 mM, Figure 2C). These results suggest that 2–10 mM TRF2B was required to form wellshifted DNA species during electrophoresis but was not enough to form DNA complexes large enough to detect in the centrifugation assay
Summary
The eukaryotic genome is packaged into complex nucleoprotein structures known as chromatin. The basic unit of chromatin structure is the core nucleosome, comprised of a histone octamer wrapped within 1.67 left-handed superhelical turns. Arrays of core nucleosomes are capable of folding into compact higher-order structures, a process facilitated by other chromatin architectural proteins such as linker histones. The ends of eukaryotic chromosomes, have a unique chromatin structure involving specific telomere binding proteins [8,9]. In vitro studies show that nucleosomes slide more readily along telomeric DNA relative to nucleosome positioning sequences [14]. Together, these findings suggest that telomeric chromatin has unique properties
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
