A grand unified model with $M_G\sim M_{string}$ and $M_I\sim 10^{12}$   GeV
  We present a model based on the gauge group SU(2)_L\times SU(2)_R \times SU(4)_C with gauge couplings that are found to be unified at a scale near the string unification scale. This model breaks to the MSSM at an intermediate scale which is instrumental in producing a neutrino in a mass range that can serve as hot dark matter and can also solve the strong CP problem via a harmless invisible axion. 
N.G. Deshpande, B. Dutta, and E. Keith