Rabbit Anti-HIV PEG10 Polyclonal antibody for WB. Murine leukemia viruses belong to family of Retroviruses group and are named for their ability to cause cancer in mice. Some form of MLV's are used in cancer research. The retroviral Gag protein plays important roles at several stages in the viral life cycle. Late in infection, the Gag precursor protein acts to mediate the assembly and release of virion particles. After budding, the core matures by cleavage of Gag precursor protein into the mature core proteins, the matrix (MA), capsid (CA) and nucleocapsid proteins. These separated Gag proteins then play roles in the early stages of infection.