An object of the present invention is to provide an electrodeposition paint composition and a method of forming an electrodeposited coating, which exhibit quality of coating deposition even in the interior of narrow spaces of objects subjected to painting. The present invention provides a master batch of an organic peroxide in which the organic peroxide is so uniformly dispersed in a thermoplastic resin that crosslinking andor decomposition occur uniformly, a method of preparing the same, a thermoplastic resin composition obtained using the master batch and a method of preparing the same. Polynucleotides encoding the novel leader peptides and a method of designing the polynucleotides are described.