This is a positive control vector for monitoring transfection efficiency in mammalian cells. The plasmid contains the E. coli LacZ gene, which encodes the enzyme beta-galactosidase. The activity of beta-galactosidase can be measured in cell extracts with great sensitivity and precision using the substrate ONPG, or examined by X-gal staining of transfected cells. This plasmid is also the control vector in SpeAd kits (#K1000 and #K1100).