[en] The Grand Unification Theory with the (SU₅ circle-times U₁)circle-times(SU₃ circle-times U₁)_H gauge group, in which (SU₃ circle-times U₁)_H is the horizontal symmetry of quark-lepton generations, is considered within the framework of the approach using a four-dimensional superstring with free fermions. The horizontal hypercharge Y_H is used to quantize electromagnetic charges of quarks and leptons within the framework of standard SO₁₀ 16-plets. In the authors approach, construction of the horizontal gauge symmetry leads to the appearance of a new massive SO₁₀ 16-plet, which is a singlet with respect to the horizontal group. The resulting Higgs sector may enable the hidden gauge group to be suppressed significantly and to break the flip SU₅ circle-times U₁ symmetry first to SM and then to SU^c₃ circle-times U^em₁. The Q_em construction allows the authors to avoid states with exotic charges (Q^ex_em = 1/nQ_em), whose emergence is characteristic of the approach using four-dimensional superstrings. In the authors approach, the horizontal group can be violated in the low-energy limit, which offers a possibility for the existence of a superweaklike mechanism of CP violation in the gauge sector of the SU_3H group. 19 refs., 2 tabs