  We consider restrictions imposed on the electromagnetic and weak current
operators by Poincare invariance and show that some assumptions used in
deriving the sum rules in deep inelastic scattering (DIS) have no physical
ground. In particular there is no ground to neglect the contribution of
nonperturbative effects to these operators, even in the Bjorken limit.
Therefore the conclusion that the sum rules in DIS unambiguously follow from
QCD is not substantiated.
