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Comparison between TRF2 and TRF1 of their telomeric DNA‐bound structures and DNA‐binding activities

Mammalian telomeres consist of long tandem arrays of double‐stranded telomeric TTAGGG repeats packaged by the telomeric DNA‐binding proteins TRF1 and TRF2. Both contain a similar C‐terminal Myb domain that mediates sequence‐specific binding to telomeric DNA. In a DNA complex of TRF1, only the single Myb‐like domain consisting of three helices can bind specifically to double‐stranded telomeric DNA. TRF2 also binds to double‐stranded telomeric DNA. Although the DNA binding mode of TRF2 is likely identical to that of TRF1, TRF2 plays an important role in the t‐loop formation that protects the ends of telomeres. Here, to clarify the details of the double‐stranded telomeric DNA‐binding modes of TRF1 and TRF2, we determined the solution structure of the DNA‐binding domain of human TRF2 bound to telomeric DNA; it consists of three helices, and like TRF1, the third helix recognizes TAGGG sequence in the major groove of DNA with the N‐terminal arm locating in the minor groove. However, small but significant differences are observed; in contrast to the minor groove recognition of TRF1, in which an arginine residue recognizes the TT sequence, a lysine residue of TRF2 interacts with the TT part. We examined the telomeric DNA‐binding activities of both DNA‐binding domains of TRF1 and TRF2 and found that TRF1 binds more strongly than TRF2. Based on the structural differences of both domains, we created several mutants of the DNA‐binding domain of TRF2 with stronger binding activities compared to the wild‐type TRF2.