LOCALIZATION OF A SPECIFIC NUCLEOTIDE IN YEAST TRANSFER-RNA BY SCANNING-TRANSMISSION ELECTRON-MICROSCOPY USING AN UNDECAGOLD CLUSTER

Scanning transmission electron microscopic images of transfer RNAs reveal the molecular dimensions and compact morphology of these small macromolecules in unprecedented detail. Selective labeling of a sulfhydryl group on 2-thiocytidine enzymatically inserted at position 75 at the 3′ end of yeast tRNAPhe, with an undecagold cluster permits identification of this specific tRNA site by dark field STEM. Imaging of a single nucleotide at a defined location on the tRNA molecule should make it possible to localize in situ tRNAs at the A, P, and E sites of the ribosomal peptidyl transferase center, and in complexes of tRNA with enzymes and elongation factors. In addition, this approach may be used for the highly specific topographical mapping of other RNAs and/or biological macromolecular complexes. © 1991.