Editing Reporter gene (section)

==Transformation and Transfection Assays==
Many methods of [[transfection]] and [[Transformation (genetics)|transformation]] – two ways of expressing a foreign or modified gene in an organism – are effective in only a small percentage of a population subjected to the techniques. Thus, a method for identifying those few successful gene uptake events is necessary. Reporter genes used in this way are normally expressed under their own [[Promotor (biology)|promoter]] (DNA regions that initiates gene transcription) independent from that of the introduced gene of interest; the reporter gene can be expressed [[Gene expression|constitutively]] ("always on") or [[Gene expression|inducibly]]. This independence is advantageous when the gene of interest is expressed under specific or hard-to-access conditions.<ref name=":5" />

Reporter genes employ diverse mechanisms to visualize or quantify gene activity:

* '''Enzymatic reporters''' (e.g., ''LacZ'') encode enzymes that catalyze reactions yielding a visible product. For example, β-galactosidase (encoded by ''LacZ'') cleaves X-gal to produce a blue color, allowing easy identification of successful gene disruption (white colonies) versus intact genes (blue colonies).<ref name=":6" />
* '''Bioluminescent reporters''' (e.g., luciferase) produce light via chemical reactions, enabling live-cell imaging and promoter studies without external light sources.<ref name=":7" />
* '''Colorimetric reporters''' (e.g., ''CAT'') generate detectable color changes when enzymes react with substrates, measurable via spectrophotometry or TLC.<ref name=":8" />
* '''Selectable markers''' (e.g., ''Neo'') confer antibiotic resistance (e.g., to G418), ensuring only transformed cells survive in selective media.<ref name=":9">{{Cite journal |last=Smale |first=Stephen T. |date=2010-05-01 |title=β-Galactosidase Assay |url=https://cshprotocols.cshlp.org/content/2010/5/pdb.prot5423 |journal=Cold Spring Harbor Protocols |language=en |volume=2010 |issue=5 |pages=pdb.prot5423 |doi=10.1101/pdb.prot5423 |issn=1940-3402 |pmid=20439410|url-access=subscription }}</ref><ref>{{Cite journal |last1=Franke |first1=C A |last2=Rice |first2=C M |last3=Strauss |first3=J H |last4=Hruby |first4=D E |date=August 1985 |title=Neomycin resistance as a dominant selectable marker for selection and isolation of vaccinia virus recombinants. |journal=Molecular and Cellular Biology |language=en |volume=5 |issue=8 |pages=1918–1924 |doi=10.1128/MCB.5.8.1918 |issn=0270-7306 |pmc=366908 |pmid=3018537}}</ref>

In the case of selectable-marker reporters such as ''CAT'', the transfected population can be grown on a chloramphenicol-containing substrate. Only cells with the ''CAT'' gene survive, confirming successful transformation.<ref name=":10" />