This type of labeling allows scientists to study DNA or RNA in their structure, function, or formation with other nucleic acids.[2] The first base modification for fluorescent labeling occurred in 1971 with a 4-thiouridine and 4-thiouracil.[3] This research along with others, which included various types of direct and non-direct labeling via: analogs, addition via enzymes, or other methods made labeling of nucleotides much safer for scientist to study DNA.[2]