Yes, luciferase can be used as a plasmid. The luciferase is driven by a promoter that is strong and constitutive. The expression of luciferase as a second promoter allows it to be used as a plasmid. Luciferase can also feature in when dealing with reporter plasmids. Luciferase-containing plasmids are commonly used to investigate the effect of regulatory elements, such as promoters, enhancers and untranslated regions, or the effect of mutations of these regulatory elements on gene expression.