Luciferase Gene (lux).
In the presence of a suitable substrate, the enzyme luciferase confers on the organism carrying it, the ability to glow in the dark. In other words the organism carrying this enzyme exhibits luminiscence on an assay for the enzyme luciferase. The enzyme luciferase differs in bacteria and firefly. While in bacteria, it consists of two peptide subunits coded-by genes luxAand luxB, in firefly it consists of a single polypeptide coded by a gene lux. The enzyme luciferase in these two systems uses different substrates for luminiscence. Therefore, depending upon the source of luciferase gene used as a scoreable marker gene, the assay for detection of its presence also differs. When the source of the gene is bacteria, the substrate used is an aldehyde (decanal), which is supplied exogenously with FMNH₂. Alternatively, when the source is firefly, luciferin (a heterocyclic carboxylic acid) is instead used as a substrate, and is supplied with ATP and oxygen.