  We show that both the k_T- and collinear factorization for the DIS structure
functions can be obtained by consecutive reductions of the Compton scattering
amplitude. Each of these reductions is an approximation valid under certain
assumptions. In particular, the transitions to the k_T- factorization is
possible when the virtualities of the partons connecting the perturbative and
non-perturbative blobs are space-like. Then, if the parton distribution has a
sharp maximum in k_T, the k_T factorization can be reduced to the collinear
factorization.
