Transcription and Translation in Train: In bacteria, translation of messenger RNA into proteins by the ribosome usually begins soon after the ribosome binding site emerges from RNA polymerase. Now there is evidence for direct coupling between transcription and translation in bacteria. Proshkin et al. (p. 504 ; see the Perspective by Roberts ) show that the trailing ribosome controls the rate of transcription by preventing RNA polymerase from spontaneous backtracking, which allows precise adjustment of transcriptional yield to translational needs under various growth conditions. Burmann et al. (p. 501 ; see the Perspective by Roberts ) provide a potential mechanism for coupling by showing that the transcription factor NusG, which binds RNA polymerase through its amino-terminal domain, competitively binds either a ribosomal protein or the Rho transcription termination factor through its carboxy-terminal domain. Rho binding might occur after release of the ribosome from messenger RNA, thus linking termination of transcription and translation.

Resistance to proteolytic enzymes and heat is thought to be a prerequisite property of food allergens. Allergens from peanut (Arachis hypogaea) are the most frequent cause of fatal food allergic reactions. The allergenic 2S albumin Ara h 2 and the homologous minor allergen Ara h 6 were studied at the molecular level with regard to allergenic potency of native and protease-treated allergen. A high-resolution solution structure of the protease-resistant core of Ara h 6 was determined by NMR spectroscopy, and homology modelling was applied to generate an Ara h 2 structure. Ara h 2 appeared to be the more potent allergen, even though the two peanut allergens share substantial cross-reactivity. Both allergens contain cores that are highly resistant to proteolytic digestion and to temperatures of up to 100 °C. Even though IgE antibody-binding capacity was reduced by protease treatment, the mediator release from a functional equivalent of a mast cell or basophil, the humanized RBL (rat basophilic leukaemia) cell, demonstrated that this reduction in IgE antibody-binding capacity does not necessarily translate into reduced allergenic potency. Native Ara h 2 and Ara h 6 have virtually identical allergenic potency as compared with the allergens that were treated with digestive enzymes. The folds of the allergenic cores are virtually identical with each other and with the fold of the corresponding regions in the undigested proteins. The extreme immunological stability of the core structures of Ara h 2 and Ara h 6 provides an explanation for the persistence of the allergenic potency even after food processing.

The human immunodeficiency virus type 1 Vpu protein enhances virus particle release from infected cells, decreases the tendency of syncytia formation and induces degradation of human CD4 receptor. It is known that the cytoplasmic part of Vpu is responsible for direct interaction to and degradation of CD4. The tertiary fold of the Vpu cytoplasmic domain in aqueous solution was determined employing NMR spectroscopy and molecular‐dynamics simulated‐annealing protocols. We found a very well defined amphipathic α‐helix in the membrane proximal part (40–50), a less well defined helix (60–68), and a short α‐helix at the C‐terminus (75–79). We further determined the overall tertiary structure based on long‐range nuclear Overhauser enhancement effects. Correlation of results from mutation experiments of Vpu and the structure data is discussed.

The human c-Ha-ras protooncogene product p21C was truncated at the C terminus by 23 amino acids. The resulting G-binding domain, p21 (1-166) = p21C', can be crystallized as a complex with the slowly hydrolyzing GTP analogues guanosin-5'-[beta,gamma-imido]triphosphate, guanosin-5'-[beta,gamma-methylene]triphosphate, and guanosin-5'-O-(3-thiotriphosphate). We show here that this protein has biochemical properties very similar to those of the intact protein. Activating mutations in position 12 (Gly12----Val; Gly12----Arg) have the same effect on the properties of the truncated protein as on intact protein. Nuclear magnetic resonance (NMR) measurements show no apparent effect of the C-terminal deletion on the solution structure of p21. This suggests that neither the structure of the G-binding domain nor any of its biochemical properties are markedly influenced by the truncation.