Analysis of the spin structure function $g_2(x,Q^2)$ and twist-3 operators

We discuss the spin-dependent structure function $g_2(x,Q^2)$ in the framework of the operator product expansion. It is noted that the anomalous dimensions and coefficient functions for the twist-3 gluon-field-dependent operators depend on the choice of the operator basis. The role played by the operators proportional to the equation of motion is clarified.