Rad50 (unknown)

Figure 4 Schematic diagram of domains of interactions for hTRFl and hTRF2. The solid lines indicate the portion/s of TRF1 (A) and TRF2 (B) required for interaction with the particular telomere associated factor.

telomeric organization such as bouquet formation and telomeric condensation. Owing to the high degree of identity between the DNA-binding domains of TRF1 and TRF2, it is thought that the minimum binding site of TRF2 is equivalent to that of TRF1, but this has not been proved experimentally. Whether or not TRF2 dimers are able to pair distant half sites has not been addressed. Further pairing properties of these proteins is discussed below (t-loops).

Recent evidence suggests that the DNA end-binding protein Ku can associate with mammalian telomere ends both in vivo and in vitro (105,106). Ku is a het-erodimer of a 70-Kd and an 80-Kd subunit and was first identified as being in-

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