IMMUNODETECTION OF RNA ON ULTRA-THIN SECTIONS INCUBATED WITH POLYADENYLATE NUCLEOTIDYL TRANSFERASE

A new method is described for locating RNA on ultra-thin sections. Sec tions of aldehyde-fixed, plastic-embedded cells were incubated in a me dium containing polyadenylate nucleotidyl transferase (PnT) and biotin ylated ATP. The labeled nucleotides bound to RNA at the surface of the ultra-thin sections were than visualized by an indirect immunogold la beling technique. The resulting labeling pattern was dependent on the presence of divalent cations in the PnT medium. The method revealed wi th great precision the specific RNA-containing structures within Ehrli ch tumor cells. The method is applicable to Epon sections. However, th e labeling intensity varies according to the fixation used. Best resul ts were obtained on acetylated cell sections. The method can be combin ed with EDTA regressive staining. The in situ PnT method provides a ve ry useful tool for pinpointing the precise location of RNA within biol ogical material at the ultrastructural level.