OFPSparkTM is a red (orange) fluorescent protein (excitation/emission maxima are 549 and 566 nm, respectively) derived from DsRed. Possessing high photostability and pH stability, OFPSparkTM is more than twice brighter than mOrange2. Fast OFPSparkTM maturation makes it detectable in mammalian cells as early as within 8 hrs after transfection. OFPSparkTM can be expressed and detected in a wide range of organisms. Mammalian cells transiently transfected with OFPSparkTM expression vectors produce bright fluorescence in 8 hrs after transfection. No cytotoxic effects or visible protein aggregation are observed. For its monomer structure, OFPSparkTM performs well in some fusions and protein labeling applications.