A method for producing picornaviral capsid protein complexes (e.g., picornavirus like particles) inE. coliusing a small-ubiquitin-related fusion protein expression system and anE. colistrain used in practicing this method. Also disclosed is use of the picornaviral capsid protein complexes like thus prepared for eliciting immune responses.本發明係關於一種於大腸桿菌內利用小泛素相關融合蛋白表現系統製備小RNA病毒外殼蛋白複合體(例如,類小RNA病毒顆粒)的方法,以及用於實施此方法的大腸桿菌株。本發明亦揭示一種據此製備而得之小RNA病毒外殼蛋白複合體之用於誘發免疫反應的用途。