To specifically analyze the effect of IN mutants in early steps of viral infection, we modified a previously described HIV-1 single-cycle replication system [32] and constructed a RT/IN/Env gene-deleted HIV-1 provirus NLlucΔBglΔRI, in which the nef gene was replaced by a firefly luciferase gene [33]. The gene discussed is ERVW-1; the disease is viral infectious disease.