  The Peccei-Quinn symmetric extension of the missing-partner model in the
supersymmetric SU(5) grand unified model is consistent with the observed
stability of the proton, even in the large $\tan\beta$ region ($\simeq 50-60$)
expected from the Yukawa unification. Moreover, the SU(5) gauge coupling
constant remains small enough for the perturbative description of GUT's below
the gravitational scale.
