Abstract: Provided are four new fluorescent proteins. The proteins were derived from two wild-type fluorescent proteins: a red fluorescent protein (RFP) that was isolated from Actinodiscus or Discosoma sp. 1 and a green fluorescent protein (GFP) isolated from Montastraea cavernosa. Two mutant forms were generated from each wild-type protein. Each of the mutated forms has a higher fluorescence intensity than the respective wild-type form. The mutant forms of the fluorescent proteins allow for more sensitive detection of the fluorescence emitted by the proteins. Additionally, one of the mutant proteins is more resistant to photobleaching than its wild-type protein. The invention also encompasses isolated nucleic acids encoding the mutant forms of the wild-type RFP and GFP.