  We present a novel way of realizing the pseudo-Nambu-Goldstone boson
mechanism at all orders in perturbation theory, for the doublet-triplet
splitting in supersymmetric grand unified theories. The global symmetries of
the Higgs sector are attributed to a non-vectorlike Higgs content, which is
consistent with unbroken supersymmetry in a scenario with flat extra dimensions
and branes. We also show how in such a model one can naturally obtain a
realistic pattern for the Standard Model fermion masses and mixings.
