Radial mass density functions of vitrified helical specimens determined by scanning transmission electron microscopy: their potential use as substitutes for equatorial data

S. Trachtenberg*, K. R. Leonard, W. Tichelaar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Using STEM dark field images, we have determined linear mass densities and radial density profiles of vitrified helical particles. The samples studied are: TMV, RNA-free helical polymers of TMV coat protein (TMV-P), Salmonella typhimurium bacterial flagellar filaments and Escherichia coli pili. The difference between the profiles obtained for TMV and TMV-P shows a maximum at a radius of about 4 nm, corresponding to the RNA in TMV. Of the peaks that are resolved in X-ray diffraction analysis we can resolve the ones for TMV at radii of ~4.2 and ~6.7 nm and a shoulder at ~7.8 nm. Density peaks in bacterial flagellar filaments appear at radii of ~4.2, ~6.5, ~8.5, and ~10.5 nm. Accurate mass data can be obtained if the filaments are embedded in ice layers of uniform thickness; their diameters need to be similar to that of the mass standard (TMV) when these data are measured in a comparative manner. Ice layers are often not uniform, and thickness variations are well revealed in STEM dark field. The signal-to-noise ratio and contrast for the transverse projections are lower than those measured for freeze-dried specimens: half an order and one order of magnitude, respectively. The thinnest uniformly thick ice layer still containing a single layer of particles is ~10-15 nm thicker than the particles. Radial mass density functions that are directly determined in STEM may have a potential use as substitutes for the unreliable equatorial data in helical reconstructions of TEM bright field images of vitrified specimens.

Original languageEnglish
Pages (from-to)307-321
Number of pages15
JournalUltramicroscopy
Volume45
Issue number3-4
DOIs
StatePublished - 1 Nov 1992

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