The products of interaction of pyronine Y (PY) with dsRNA and DNA are fluorescent (emission in orange color wavelength).. In the presence of Hoechst 33342, however, the PY-associated fluorescence of DNA is suppressed. Therefore, when combined with Hoechst 33342 PY stains dsRNA with relatively good specificity. Of course, one can remove DNA by incubation with DNase and then use PI or PY to stain dsRNA. It should be noted that fluorescence of PY-dsRNA complexes is seen only at PY concentration below 300 uM. At higher PY concentration the fluorescence of dsRNA decreases due to condensation of RNA caused by PY (Cytometry, 8:136-145, 1987). Zbigniew Darzynkiewicz Brander Cancer Research Institute New York Medical College 19 Bradhurst Ave. Hawthorne, NY 10532 tel: 914-347-2801 fax: 914-347-2804 http://www.geocities.com/z_darzynkiewicz
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