mRuby3 is a monomeric red fluorescent protein with an excitation peak of 558nm and an emission peak of 592nm. It is an artificial derivative of the naturally occurring fluorescent protein encoded by the Entacmaea quadricolor eqFP611 gene, obtained by mutagenesis of mRuby2, being both more photostable and brighter than mRuby2 (PMID:26879144).