  A new scaling variable is introduced in terms of which nuclear shadowing in
deep-inelastic scattering is universal, i.e. independent of $A$, $Q^2$ and $x$.
This variable can be interpreted as a measure of the number of gluons probed by
the hadronic fluctuations of a virtual photon during their lifetime. According
to recent data from the H1 and ZEUS experiments, the gluon density in a proton
rises steeply as $x$ tends to zero. So nuclei which in the infinite momentum
frame have a large surface density of gluons model at larger $x$ values what we
expect for the proton at much smaller $x$. Using experimental information on
nuclear shadowing we predict the unitarity corrections to the proton structure
function at small $x$ and extract the bare Pomeron intercept.
