## Minimal Sufficiency Question

I'm having trouble figuring this out, but I'm pretty sure it is only a few lines for someone who understands this a little better:

"Suppose that $T_1$ is sufficient and $T_2$ is minimal sufficient. Let $U$ be an unbiased estimator of $\theta$ and define $U_1 = E(U|T_1)$ and $U_2 = E(U|T_2)$. Show that $U_2 = E(U_1|T_2)$."