Nucleic acid molecules encoding monomeric near-
infrared fluorescent proteins, variants and derivatives thereof are provided, as well as proteins and peptides encoded by these nucleic acids. Also provided are proteins that are substantially similar to, or derivatives, homologues, or mutants of, the above-referenced specific proteins. Also provided are fragments of the nucleic acids and the peptides encoded thereby, specifically split fluorescent proteins. In addition, host-cells, stable
cell lines and transgenic organisms comprising above-referenced
nucleic acid molecules are provided. The invention also refers to methods of making and using monomeric fluorescent proteins derived from bacterial phytochromes. The subject
protein and
nucleic acid compositions find use in a variety of different applications and methods, particularly for labeling of biomolecules, cells or
cell organelles, and for detecting
protein-
protein interactions. Finally, kits for use in such methods and applications are provided.