Although the EDTA regressive technique allows the visualization of RNPs, this widely used method is not intended to be specific for RNA alone. A fine ultrastructural visualization of RNA on ultrathin sections can be obtained with terbium citrate: this method gives a weak contrast but a very fine end product which allows observations at a high resolution level.
The procedure is very simple since it consists only of a period of incubation and very short washes, which are the crucial point of this technique to avoid the Tb removal from RNA. This method does not require any special type of fixation and embedding.
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