  We argued that deep inelastic scattering (DIS) at small values of Q squared
is an essentially nonperturbative process and can be described, partially at
least, by the vector meson dominance (VMD) model. We showed by the
straightforward calculation that VMD model alone can successfully explain data
on structure functions of DIS in a broad interval of x (5e-2 - 1e-4) for the
region Q squared < 1 GeV squared. For a description of data at larger Q squared
we used the two-component (VMD + perturbative QCD) approach. We showed that
these two components can be separated if VMD is used in the aligned jet
version. We took into account, in calculations of VMD component of structure
functions, the excited states of the rho-meson and nondiagonal transitions
between different members of the rho-meson family. Amplitudes of these
transitions were obtained using a formalism of the light-front Bethe-Salpeter
equation and the method of diffraction-scattering eigenstates. The perturbative
QCD component was calculated using a framework of the colour dipole model with
the dipole cross section having a Regge-type energy dependence. We presented
results of the detailed comparison of our predictions with experimental data
for structure functions of the nucleon. We obtained also approximate
predictions for the structure functions in the region of very small x, up to
1e-9, and showed that nonperturbative component at such values of x is still
relatively large and must be taken into account if Q squared is about few GeV
squared or less.
