A mechanism of formation, of all interelectrode current based on a resonant tunneling through localized electronic levels of a. single molecule is proposed. It is shown that, an external electric field applied to a. molecule brings to the transformation of extended molecular orbitals into localized molecular orbitals. It results in the essential modification of nonlinear current-voltage characteristics of the molecule. Local voltage division factors reflecting the partial voltage biases within a molecule are specified, and an. analytic expression for the I-V characteristics of a two-site molecule is derived.