  We augment the Minimal Supersymmetric Standard Model with a gauged
family-dependent $U(1)$ to reproduce Yukawa textures compatible with
experiment. In the simplest model with one extra chiral electroweak singlet
field, acceptable textures require this $U(1)$ to be anomalous. The
cancellation of its anomalies by a generic Green-Schwarz mechanism requires
$\sin^2\theta_w=3/8$ at the string scale, suggesting a superstring origin for
the standard model.
