Source : Escherichia Coli. The E.coli derived recombinant protein contains the Nucleocapsid protein 1-49 amino acids immunodominant regions. The SARS Nucleocaspid is a protein that has a crucial structural importance, by making the virions associates with the RNA genome and therefore create a nucleocapsid that has the specific helical form. There has been found 3 different domain structures to the nucleocapsid antigen. This protein contains 3 outer structural proteins, the membrane (M), envelope (E), and spike (S) proteins.