  A rest frame valence quark model is applied to the deep inelastic scattering
of charged leptons by protons. The parameters of the model are determined by a
fit to unpolarized electron cross sections. The model then can be used to
calculate the asymmetry in polarized deep inelastic scattering. The predicted
spin-dependent structure function g1p is in good agreement with recent
measurements. This indicates that, in the proton rest system, the spin of the
proton is carried by the valence quarks.
