In conclusion, these results indicate that (1) Box1 is fully dispensable for binding to XD and induced folding, (2) Box2 is strictly required for induced folding to take place, and (3) Box3 contributes to binding to XD, as pointed out by the reduced ability of N TAILD3 to undergo induced folding. Moreover, the fact that N TAILD3 , N TAILD1 , and N TAIL Bourhis et al. 2004) share similar folding propensities suggests that the contribution of Box3 to the interaction can be accounted for more in terms of binding rather than of induced folding.