Table 1 Characteristics of StayGold and reference green-emitting FPs

Protein	λab^a/λem^b (nm)	ε^c (10³ M⁻¹ cm⁻¹)		QY_f^d	Brightness		Photostability t_1/2 (s)^g			Protein yield^h (mg L⁻¹)
		ε^c (10³ M⁻¹ cm⁻¹)			Brightness		Protein	Expressed in living cells
		λab	488		Mol^e	Cell^f	Protein	HBSS	DMEM
StayGold	496/505	159	105	0.93	148	2.06	11,487	9,919	12,421	194
EGFP	488/509	51	51	0.71	36	1.00	700	493	481	93
SiriusGFP	502/516	54	35	0.19	10	0.45	477	522	558	127
mClover3	505/518	99	52	0.84	83	1.73	289	116	66	137
mNeonGreen	505/518	112	64	0.87	97	2.05	176	265	335	172

^aAbsorbance maximum. ^bEmission maximum. ^cAbsolute extinction coefficient at λab (left) and 488 nm (right). The measurement was based on the fact that, after alkali denaturation of these FPs, the chromophore, containing a dehydrotyrosine residue conjugated to the imidazolone group, absorbs light maximally at 447 nm with a molar extinction coefficient of 44,000 M⁻¹ cm⁻¹ (ref. ¹⁹). See Supplementary Fig. 4a. ^d Fluorescence quantum yield measured using an absolute photoluminescence quantum yield spectrometer. ^eProduct of ε (λab) and QY_f. This value reflects the molecular brightness of an FP. ^fCellular brightness calculated from data shown in Supplementary Fig. 7b. The fluorescence from each green-emitting FP (with excitation at 488 nm) was corrected by mCherry fluorescence and then normalized to that of EGFP (ref. ⁴³). Equimolar co-expression of a green-emitting FP and mCherry using the bicistronic expression system⁴⁴. ^gTime in seconds to reduce emission rate from 1,000 to 500 photons/s/molecule under WF illumination. ^hAmount of purified protein from 1 L of bacterial culture. All values were measured in this study. SiriusGFP is a variant of EGFP that exhibits a two-fold increase in photostability relative to EGFP but a three-fold decrease in brightness²⁰.

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