In exhaust gas purification system including catalyst unit carrying a NOx occlusion-reduction type catalyst, a first-stage rich control having a target air-fuel ratio lower than theoretical air-fuel ratio is conducted through addition of the amount of reducing agent meeting the amount of oxygen emitted in the initial stage of regeneration control. The method includes providing a metal substrate, a metal implanting component including a connecting part disposed thereon; bonding the metal implanting component to the metal substrate; and forming a plastic component on the metal substrate by an insert molding process. In one embodiment of the invention, expression of an endogenous gene is activated or increased following integration into the cell, by non-homologous or illegitimate recombination, of a regulatory sequence that activates expression of the gene.