  An analytical formalism, including RG running at two loop order, is used to
link the supersymmetric and GUT spectra in any GUT model in which the three
gauge couplings unify. In each specific GUT model, one can then fully explore
the interplay between the pattern of supersymmetry breaking and the prediction
for the proton lifetime. With this formalism at hand, we study three concrete
GUT models: (i) Minimal SU(5) SUSY GUT, (ii) Missing Partner SU(5) SUSY GUT,
and (iii) an orbifold SU(5) SUSY GUT. In each case we derive interesting
conclusions about the possible patterns of the supersymmetric spectrum once the
present limits on the proton lifetime are imposed, and vice versa, we obtain
the predictions for the proton lifetime for specific viable choices of the SUSY
spectrum.
