THE ADSORPTION STAINING TECHNIQUE APPLIED TO ISOLATED PREMESSENGER RIBONUCLEOPROTEIN-PARTICLES - A COMPARISON WITH CONVENTIONAL TECHNIQUES USING ELECTRON-MICROSCOPE TOMOGRAPHY

A specific type of premessenger RNP particle, Balbiani ring granules f rom the dipteran Chironomus tentans, was biochemically isolated and vi sualized in three dimensions with electron microscope tomography. The particles were prepared for electron microscopy in three different way s: positively stained, negatively stained and adsorption-stained (embe dded in polyvinyl alcohol, PVA, and concomitantly stained). The result s were compared with those obtained for RNP particles studied in situ in ultrathin sections of plastic-embedded cells. The positively staine d particles were compacted and heavily deformed with little or no inte rnal structure. The negatively stained and the adsorption-stained part icles were well preserved; the outer contours and the central cavities of the particles were outlined. The internal structure, i.e. the fold ed 7-nm elementary fibre, could not be recognized in the negatively st ained particles. In the adsorption-stained particles, however, the fib re was discernable, although not quite as distinctly demarcated as in the plastic-embedded samples. We conclude that embedding in PVA with c oncomitant staining with uranyl acetate is a rapid method to obtain bo th good preservation and staining of isolated RNP particles. The PVA-e mbedded particles were also found to be sufficiently resistant to irra diation to permit a comprehensive tilt-series to be taken for electron microscope tomography.