Higher-order Multimers Research Articles

Genetic evidence that the Tat proteins of human immunodeficiency virus types 1 and 2 can multimerize in the eukaryotic cell nucleus.

The formation of dimers or higher-order multimers is critical to the biological activity of many eukaryotic regulatory proteins. However, biochemical analyses of the multimerization capacity of the Tat trans activator of human immunodeficiency virus types 1 (HIV-1) and 2 (HIV-2) have yielded contradictory results. We used the two-hybrid genetic assay for protein-protein interactions in the eukaryote Saccharomyces cerevisiae (S. Fields and O.-K. Song, Nature [London] 340:245-246, 1989) to examine the multimerization of Tat in vivo. Both HIV-1 and HIV-2 Tat are shown to form specific homo- but not heteromultimers in the yeast cell nucleus. Mutational analysis indicates a critical role for the essential core motif of Tat in mediating this interaction but demonstrates that efficient Tat multimerization does not require an intact cysteine motif. These data raise the possibility that the multimerization of Tat may be important for Tat function in higher eukaryotes.

ChemInform Abstract: Structure and Dynamics of Olefin Radical Cation Aggregates. Time‐Resolved Fluorescence Detected Magnetic Resonance

The time-resolved EPR spectra and thus the structure and dynamics of transient hydrocarbon radical cations are obtained by the pulse radiolysis-fluorescence detected magnetic resonance (FDMR) technique. Here the authors report the observation of short-lived radical cations from olefins. FDMR-EPR spectra of radical cations from tetramethylethylene and cyclohexadiene are illustrated. The olefin radical cations, FDMR spectra are concentration-dependent, since dimerization with neutral molecules takes place at higher (>10/sup -2/ M) olefin concentration. Rate constants for the dimerization reaction are derived and the effect of solvent viscosity on aggregate formation is demonstrated. By monitoring the further reactions of dimer cations the authors have obtained EPR evidence for previously unobserved higher-order (multimer) radical cation aggregates of olefins. 16 references, 5 figures.

Peptide mapping by limited proteolysis in sodium dodecyl sulfate of the main intrinsic polypeptides isolated from human and bovine lens plasma membranes

The major intrinsic lens plasma membrane protein isolated from calves, young cows and young humans, is an approx. 26 000 dalton protein. In the adult human lens, a second major intrinsic protein ( M r 22 000 ) is found. The relationships between the bovine 26 000 dalton protein and the human 26 000 dalton protein, as well as between the human 26 000 dalton protein and the human 22 000 dalton protein, were examined using peptide mapping by limited proteolysis is sodium dodecyl sulfate. Purified membrane proteins were obtained by preparative sodium dodecyl sulfate gel electrophoresis. At concentrations of 1 mg/ml or more, the purified 26 000 dalton and 22 000 dalton proteins tend to aggregate in sodium dodecyl sulfate solution and form dimers, trimers and tetramers, as well as higher-order multimers. These aggregates cannot be dissociated by β-mercaptoethanol. Staphylococcus aureus protease exhibits differential proteolytic activity toward the intrinsic major plasma membrane proteins and the soluble lens proteins which are difficult to remove from membrane preparations. While the soluble lens proteins are very effectively cleaved by S. aureus into fragments of less than 12 000 daltons, both the human and bovine 26 000 dalton major intrinsic membrane proteins lost only an approx. 4000 dalton peptide. Under the same conditions, this protease did not proteolyse the human native approx. 22 000 dalton protein. The resistance to further proteolysis of the approx. 22 000 dalton proteins which were produced by the action of the protease on the human and bovine 26 000 dalton proteins, as well as the resistance to further proteolysis under the same conditions of the native 22 000 dalton human protein, suggest that all these proteins possess similar conformation and composition. Additional proof that the human 26 000 dalton and 22 000 dalton membrane proteins as well as the bovine 26 000 dalton protein are all closely related comes from the α-chymotrypsin peptide maps obtained from the purified proteins. These results suggest that the human 22 000 dalton membrane protein is a natural cleavage product of the 26 000 dalton main intrinsic plasma membrane protein.