David McFarland asks: >Is there such a beast as a dsRNA specific dye or at least one that can be >distinguished spectrally when it binds dsRNA? How about all this and cell >permeant? Am I dreaming or is this within reach? Pyronin Y stains dsRNA reasonably specifically provided binding to DNA is blocked by addition of any of several dyes, e.g., Hoechst 33342, 7-aminoactinomycin D, methyl green. The dye is membrane permeant, although it can be pumped out if efflux pumps are active, and it is also taken up by mitochondria. However, in many cell types, notably human lymphocytes and lymphoblastoid lines, pyronin Y and Hoechst 33342 give a good bivariate RNA/DNA histogram. Publications in Blood by Edward Srour et al at Indiana U. over the past few years describe vital staining and sorting of hematopoietic cells using Hoechst 33342 and pyronin Y. While Hoechst requires UV excitation, pyronin Y excites well at 488 nm, and can be detected through the same filters you'd use for phycoerythrin. -Howard
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