Nonsupersymmetric gauge coupling unification in [SU(6)](4) x Z(4) and proton stability

We systematically study the three family extension of the Pati-Salam gauge group with an anomaly-free single irreducible representation which contains the known quarks and leptons without mirror fermions. In The context of th is model we implement the survival hypothesis, the modified horizontal surv ival hypothesis, and calculate the tree level masses for the gauge boson an d fermion fields. We also use the extended survival hypothesis in order to calculate the mass scales using the renormalization group equation. The int eracting Lagrangean with all the known and predicted gauge interactions is explicitly displayed. Finally the stability of the proton in this model is established.