  The possibility to estimate the isospin symmetry breaking effects in the
non-perturbative part of F_2 structure function of the chargeg lN
deep-pnelastic scattering, which will provide CLAS++ dewtector of the upgraded
TJNAF machine at $Q^2\approx 2 GeV^2$, is discussed. The problems of the
Gottfried sum rule extraction are also considered.
