TRF2 Binding to Telomere Nucleosomal Arrays

Telomeres are specialized nucleoprotein structures found at the end of eukaryotic chromosomes. TRF2 is a telomere DNA binding protein that has a critical role in telomere end protection. The ability of TRF2 to bind to unusual DNA structures such as the t‐loop, and the single stranded/double stranded telomere DNA junction may facilitate its binding to DNA in the form of nucleosomal arrays, and promote higher order chromatin structure through TRF2 oligomerization. We have reconstituted a 1kb DNA fragment containing 550bp of telomere DNA into chromatin and tested the binding of full length TRF2 and two truncated forms of the protein to the telomeric nucleosomal arrays. Our data indicates that TRF2 and its truncated forms bind to telomere nucleosomal arrays as well as it binds to telomere DNA. We used Analytical Agarose Gel Electrophoresis technique, to probe for conformational changes to both the telomere DNA and the nucleosomal arrays upon binding of TRF2 or truncated forms as measured by changes in surface charge density and hydrodynamic radius. Binding of TRF2 DBD to DNA results in a decrease in surface charge density and increase in radius, while binding to nucleosomal arrays causes a greater decrease in surface charge density and a decrease in radius. This indicates that the DNA binding domain by itself is capable of compacting telomere nucleosomal arrays resulting in a reduction in telomeric DNA accessibility.