Several investigators expressing the green fluorescent protein (GFP) in
bacteria have noted an enhanced fluorescent signal when bacteria are
grown at reduced temperature (28-30 oC vs conventional 37 oC incubation).
A recent publication [Lim, C.R. J. Biochem. 118:13-17 (1995)] has noted
a similar temperature dependence in yeast. These researchers have shown
that GFP, and a GFP-nucleoplasmin fusion are less fluorescent when
expressed in Saccharomyces cerevisiae at high temperatures. Both the
fluorescence intensity and levels of the chimeric protein (by Westerns)
are maximal in 15 oC cultures, and decline as the temperature is
increased to 23, 30, 33, and 37 oC. The fluorescence intensity of the
15 oC sample was ~16-fold greater than that of the 37 oC sample.
Interestingly, the GFP fusions synthesized at low temperatures retain
bright fluorescence despite a later shift to high temperatures. These
results suggest that once a functional chromophore has formed at low
temperatures it is quite stable at higher temperatures.
Similar findings have been reported in mammalian cells, where a
temperature shift from 37 oC to 33 oC is enough to enhance the
fluorescent signal [Pines, J. TIG 11:326-327 (1995)].
Has anyone made similar observations in other systems? Are these
temperature effects observed with variant GFPs, such as the S65T
mutant that acquires the ability to fluoresce more rapidly
as compared to wtGFP? Does anyone care to speculate on the
cause of this temperature dependency?
Any discussion will be most appreciated.
Steven R. Kain
CLONTECH Laboratories, Inc.
(415) 424-8222, ext.1469