  We present a five-dimensional supersymmetric SU(5) theory in which the gauge
symmetry is broken maximally (i.e. at the 5D Planck scale M_*) on the same 4D
brane where chiral matter is localized. Masses of the lightest Kaluza-Klein
modes for the colored Higgs and X and Y gauge fields are determined by the
compactification scale of the fifth dimension, M_C ~ 10^{15} GeV, rather than
by M_*. These fields' wave functions are repelled from the GUT-breaking brane,
so that proton decay rates are suppressed below experimental limits. Above the
compactification scale, the differences between the standard model gauge
couplings evolve logarithmically, so that ordinary logarithmic gauge coupling
unification is preserved. The maximal breaking of the grand unified group can
also lead to other effects, such as O(1) deviations from SU(5) predictions of
Yukawa couplings, even in models utilizing the Froggatt-Nielsen mechanism.
