TABLE 3.

Fluorescence measurements in cells synthesizing HtpG labeled with three different GFP tags

Fusion protein	Excitation at (nm):	Emission at (nm):	Relative fluorescence after heat shock
			0 min	30 min
HtpG-CFP	433	475	0	5
HtpG-YFP	513	527	0	8
HtpG-GFP+	488	510	10	25

^aThe strains expressing the three different fusion proteins were grown in Luria-Bertani medium at 37°C to mid-exponential growth phase and were then shifted to 48°C to induce a heat shock. One-milliliter samples were withdrawn immediately before and 30 min after challenge of the cells with heat stress. The cells were pelleted by centrifugation, resuspended in phosphate-buffered saline (0.1 M sodium phosphate, 1 mM MgCl₂, pH 7.0), pelleted again, resuspended in the same buffer, and kept on ice. Then 0.1 V each of optical density at 578 nm was withdrawn and pipetted into cuvettes prewarmed at 25°C, and fluorescence measurements were carried out on an FS-4010 spectrophotometer (Hitachi). The wavelengths of fluorescence excitation and emission for the three are given.