Fluorescence—Not Just for Protein Anymore, Now RNA, Too

Move over, green and related fluorescent proteins. As reported in
today’s issue of Science, at least one lab bench is aglow with
fluorescent RNAs. Researchers led by Samie Jaffrey at Cornell
University, Ithaca, New York, developed a range of RNA molecules, or
aptamers, that tightly bind fluorescent compounds similar to that in
green fluorescent protein (GFP). First author Jeremy Paige and
colleagues "evolved" RNAs in the lab that bind fluorophores such as
4-hydroxybenzlidene imidazolinone (HBI), the molecule that gives GFP its
bright fluorescence. HBI is not fluorescent by itself. The GFP protein
backbone stabilizes the molecule so that it releases absorbed energy by
emitting light, rather than through vibration.

Paige and colleagues found several RNA aptamers that not only bound
HBI and related fluorophores, but also had a range of spectral
properties. Some RNA-fluorophore combinations emitted in the blue end of
the spectrum, others green or yellow, and one even in the orange/red
end of the spectrum. One, aptly called Spinach, is just as bright as
GFP, and when spliced onto the gene for the 5S ribosomal RNA, enabled
the researchers to follow expression of the rRNA, including its
sequestration in stress granules. The latter have been linked to
neurodegenerative diseases such as amyotrophic lateral sclerosis.

Spinach is resistant to photobleaching, which is an advantage for
researchers who need to use high-intensity light or track the molecule
for long periods. These molecules give researchers an opportunity to
code RNA reporters right into the genome, and could be used to study a
whole spectrum of RNA-RNA and RNA-protein interactions.

Paige JS, Wu KY, Jaffrey SR. RNA mimics of Green Fluorescent Protein. Science 29 July 2011; 333:642-646. Abstract

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