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Human immunoglobulin G1 Van was studied by negative staining, freeze drying and high resolution shadow casting. The Fab and Fc subunits of an intact IgG1 molecule were shown to possess limited mobility. It was found that about 70% of molecules in the IgG1 Van specimen are not flat but have a tripod-like shape.

Translating 70 S ribosomes of Escherichia coli either in the pre-translocation or in the post-translocation state have been prepared by using the cell-free translation system in poly(U)-S-S-Sepharose columns [Methods Enzymol. (1979) 59, 382-398]. Electron microscopy study of the preparations has demonstrated that: (1) the mutual orientation of the ribosomal subunits in the translating ribosomes is the same as proposed by Lake for routine 30 S.50 S couples [J. Mol. Biol. (1976) 105, 111-130]; (2) the L7/L12 stalk of the 50 S subunit sticks out from the 70 S particle and does not join the 30 S subunit; (3) pre-translocation and post-translocation state ribosomes do not differ in mutual orientation of the subunits and in the position of the L7/L12 stalk, within the limits of electron microscopy resolution.

50 S ribosomal subunit derivatives without the 5 S RNA-protein complex obtained either by splitting with EDTA or by reconstitution from the 23 S RNA and proteins have been studied by electron microscopy. Removal of the 5 S RNA-protein complex is shown to affect neither the overall morphology of the larger ribosomal subunit nor the mode of its association with the small subunit.

Elongated hollow strands were revealed on raw images and averaged by the correlation method images of the 30 S subunit of the E. coli ribosome negatively stained by uranyl acetate. The tentative three-dimensional arrangement of the 'strands' and their nature are discussed.

MS2 phage RNA-directed synthesis of an N-terminal polypeptide of the phage coat protein on Escherichia coli 70 S ribosomes was initiated in a cell-free system with the N-dinitrophenyl derivative of methionyl-tRNAFMet) and performed in the absence of tyrosine, lysine, cysteine and methionine. As a result, the translating ribosomes carried peptides up to 42 amino acid residues in length with the dinitrophenyl hapten at the N-ends. Using the immune electron microscopy technique the positions of the nascent peptide N-ends on the 70 S ribosomes have been visualized. It has been found that (i) the N-ends of nascent peptides of these lengths are accessible to antibodies, (ii) the exit site of a nascent peptide is the pocket between the base of the central protuberance and the L1 ridge on the 50 S subunit, i.e. presumably its peptidyl transferase center, and (iii) the further pathway of a nascent peptide seems to proceed along the groove on the external surface of the 50 S subunit.

Non-precipitating anti-dinitrophenyl pig immunoglobulins G have been studied by negative staining, freeze-drying and high-resolution shadow casting. The general morphology of the molecules is described. The predominant conformation of antibody molecules is a tripod-like one.

Purified preparations of Q beta replicase have been studied by electron microscopy using a negative staining technique, and a three-dimensional model of the enzyme molecule has been constructed. The molecule of this four-subunit protein appears to be a compact structure having a size of 100 +/- 10 A; it is subdivided into two unequal bipartite subparticles. The conclusion has been made that all the constituent subunits, including the ribosomal protein Sl, acquire a globular conformation when associated in the replicase complex.

The internal site of 5 S RNA comprising residues A39 and U40 has been localized on the E. coli 50 S ribosomal subunit by immune electron microscopy. It has been found to be located on the interface side of the central protuberance at the position distinctly apart but very close to the position of the 5 S RNA 3'-end providing evidence for a quite compact folded conformation of the 5 S RNA in situ.

The complex of 23 S ribosomal RNA with the nine core proteins L2, L3, L4, L13, L17, L20, L21, L22 and L23 obtained either by the disassembly procedure or by reconstitution has been studied by electron microscopy. This complex is found to be very similar to the intact 50 S subunit both in size and in shape.

Small ribosomal subunits from rat liver have been studied by electron microscopy using freeze-drying and high-resolution shadow casting. The absolute hand of the asymmetric subunit has been determined and its three-dimensional model with a 'right' location of the side protuberance has been constructed. The results evidence that pro- and eukaryotic ribosomes have a unique and principally similar structural organization.

The EF-Tu-binding center of the E. coli ribosome has been localized by immunoelectron microscopy after cross-linking of the specific EF-Tu X 70 S ribosomal complex with dimethylsuberimidate. EF-Tu has been found to be in contact with the 50 S subunit in the region of the L7/L12 stalk and with the 30 S subunit in the upper part of its body on the side opposite the top of the ledge (the platform). The EF-Tu position on a model of the 70 S ribosome is presented.