  The superstring-inspired E_6 model is reduced to the supersymmetric standard
model extended by a specific U(1) factor. This choice allows for the existence
of naturally light singlet neutrinos which also mix with the known three
doublet neutrinos, thus making it possible to accommodate all present neutrino
data. Other consequences of this model are also discussed: oblique corrections
from Z-Z' mixing, phenomenology of the two-Higgs-doublet sector, and possible
scenarios of gauge-coupling unification.
