RNA and ribose are ligands for single Gr28 proteins.

<p><b>(</b>a) Terminal taste neurons expressing the Ca²⁺ sensor CaMPARI require <i>Gr28a</i> in order to respond to ribose and RNA (<i>n =</i> 4–9). Genotypes: <i>w</i>^<i>1118</i><i>; UAS-CaMPARI/+; Gr28a-GAL4/+</i> (<i>control</i>), <i>w</i>^<i>1118</i>; Δ<i>Gr28 UAS-CaMPARI/</i>Δ<i>Gr28; Gr28a-Gal4/+</i> (ΔGr28), and <i>w</i>^<i>1118</i>; Δ<i>Gr28 UAS-CaMPARI /</i>Δ<i>Gr28; Gr28a-GAL4/UAS-Gr28a</i> (<i>Gr28a rescue</i>). (b) Expression of single <i>Gr28</i> genes conveys ribose and RNA responses to fructose-sensing pharyngeal taste neurons (<i>n =</i> 4–13). Genotypes: <i>w</i>^<i>1118</i><i>; UAS-CaMPARI Gr43a</i>^<i>GAL4</i><i>/+</i> (<i>control</i>), <i>w</i>^<i>1118</i><i>; Gr43</i>^<i>GAL4</i> <i>UAS-CaMPARI/+; UAS-Gr28a/+</i> (<i>Gr28a</i>), <i>w</i>^<i>1118</i><i>; Gr43</i>^<i>GAL4</i> <i>UAS-CaMPARI/+; UAS-Gr28b</i>.<i>a/+</i> (<i>Gr28b</i>.<i>a</i>), <i>w</i>^<i>1118</i><i>; Gr43</i>^<i>GAL4</i> <i>UAS-CaMPARI/+; UAS-Gr28b</i>.<i>e/+</i> (<i>Gr28b</i>.<i>e</i>). Final concentration of all substrates was 100 mM in water except for RNA (0.5 mg/mL). Representative images of the indicated genotypes are shown above the graphs. Scale bar is 10 μm. Each bar represents the mean ± SEM of ratios of red and green fluorescence intensities. “*” represents significant differences between the preexposure (no PC light, no chemical) group and a substrate group (two-tailed Mann-Whitney U test, <i>p <</i> 0.05). The underlying data can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2005570#pbio.2005570.s007" target="_blank">S3 Data</a>. PC, photoconversion.