  We construct a $SU(3)^3$ supersymmetric gauge theory with a common gauge
coupling g. Spontaneous breaking of this gauge group at a scale
$M_X=1.3\times10^{16} $GeV gives naturally rise exactly to the Minimal
Supersymmetric Standard Model $(MSSM)$ and consequently to the experimentally
favored values of $sin^2\theta_w$ and $\alpha_s$.The gauge hierarchy problem is
naturally solved by a missing-partner-type mechanism which works to all orders
in the superpotential. The baryon asymmetry can be generated in spite of the
(essential) stability of the proton. The solar neutrino puzzle is solved by the
MSW mechanism. The LSP is a natural "cold" dark matter candidate and "hot" dark
matter might consist of $\tau$-neutrinos. This model could be thought of as an
effective $4d$ theory emerging from a more fundamental theory at a scale
$M_c=M_P/\sqrt{8\pi}$ where $a_G\equiv{g^2\over{4\pi}}$ happens to be equal to
unity.
