  We demonstrate two novel features of the sea-quark contributions to the
polarized structure functions and photoproduction cross sections, a zero sum
rule and a zero crossing point of the polarization asymmetry, which can be
traced directly to the dynamics of the perturbative tree-graph gluon-splitting
contributions. In particular, we show that the Born contribution of massive
quarks arising from photon-gluon fusion gives zero contribution to the
logarithmic integral over the polarization asymmetry $\int {d\nu \over
\nu}\Delta \sigma(\nu,Q^2)$ for any photon virtuality. The vanishing of this
integral in the Bjorken scaling limit then implies a zero gluon-splitting Born
contribution to the Gourdin-Ellis-Jaffe sum rule for polarized structure
functions from massive sea quarks. The vanishing of the polarization asymmetry
at or near the canonical position predicted by perturbative QCD provides an
important tool for verifying the dominance of the photon-gluon fusion
contribution to charm photoproduction and for validating the effectiveness of
this process as a measure of the gluon polarization $\Delta G(x,Q^2)$ in the
nucleon. The displacement of the asymmetry zero from its canonical position is
sensitive to the virtuality of the gluon in the photon-gluon fusion subprocess,
and it can provide a measure of intrinsic and higher-order sea quark
contributions.
