  The use of the differential gluon structure function of the proton ${\cal
F}(x,Q^{2})$ introduced by Fadin, Kuraev and Lipatov in 1975 is called upon in
many applications of small-x QCD. We report here the first determination of
${\cal F}(x,Q^{2})$ from the experimental data on the small-x proton structure
function $F_{2p}(x,Q^{2})$. We give convenient parameterizations for ${\cal
F}(x,Q^{2})$ based partly on the available DGLAP evolution fits (GRV, CTEQ &
MRS) to parton distribution functions and on realistic extrapolations into soft
region. We discuss an impact of soft gluons on various observables. The
x-dependence of the so-determined ${\cal F}(x,Q^{2})$ varies strongly with Q^2
and does not exhibit simple Regge properties. None the less the hard-to-soft
diffusion is found to give rise to a viable approximation of the proton
structure function F_{2p}(x,Q^2) by the soft and hard Regge components with
intercepts \Delta_{soft}=0 and \Delta_{hard}\sim 0.4.
