  In a SUSY GUT having an extra reverse doublet-triplet splitting near the GUT
scale, where the mass of an extra doublet is greater than the mass of an extra
triplet by two orders of magnitude, a low prediction of $\alpha_s$ can be
achieved through threshold corrections via the heavy scalars in the fundamental
representations, making the prediction consistent with the values being
suggested by low energy measurements. We implement this mechanism in a SUSY
SU(5) GUT minimally extended to suppress Higgsino mediated proton decay. We
also point out that as a consequence of this extension a natural scenario
arises with a large hierarchy in Yukawa couplings ($ \lambda_t / \lambda_b \sim
40$). An experimental low value of $\alpha_s(m_Z)$ along with the
non-observation of dimension-five proton decay modes at SuperKamiokande
detector will favor such an extension of the SUSY SU(5) GUT over the minimal
case.

High Energy Physics - Phenomenology