Biomedical subjects
Publications and source records attributed to B Jacrot.
The self-assembly of brome mosaic virus capsid has been studied kinetically by means of X-ray and neutron scattering. It appears to be a very fast process: for the concentrations used (5 to 8 mg/ml) the forward scattering reaches 50% of its maximal value in less than one second. Further, the assembly seems to proceed through intermediate states whose nature is still speculative.
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The interactions of yeast tRNAAsp with cognate aspartyl-tRNA synthetase have been studied in high concentrations of either sodium chloride or ammonium sulphate by fluorescence titration and small-angle neutron scattering. In solutions containing more than 1M NaCl no complex is formed and enzymatic activity is abolished. In strong contrast, however, the physical measurements showed the formation of a two-to-one tRNA-enzyme complex, with high affinity, in 1.6 M (NH4)2SO4. Aminoacylation assays under the same salt conditions showed the enzymatic fixation of aspartic acid to tRNAAsp to occur at an appreciable rate. The present study emphasizes that the effects of salts on protein-nucleic acid interactions do not depend only on ionic strength but also on the nature of the salt. This study has allowed a rational approach to the crystallisation of a functional tRNAAsp-aspartyl-tRNA synthetase complex (Giegé, Lorber, Ebel, Thierry and Moras (1980) C.R. Acad. Sci. Paris, série D, 291, 393-396).
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Small-angle neutron scattering from solutions of small RNA viruses has been used to study protein-nucleic acid organisation. In the five viruses investigated the RNA is confined to a sphere of about 100 A radius, with a central hole (with one possible exception). The interpenetration of RNA and protein varies with viruses and seems to be related to the natrue of the forces stabilising the virus.
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A new way of studying RNA-protein complexes, using neutron small angle scattering in solution, is described and was applied in the case of the system, yeast valyl-tRNA synthetase, interacting with its cognate and non cognate yeast tRNAs. It was shown that, when limited amounts of tRNA (either cognate or non cognate) are added to valyl-tRNA synthetase, a complex consisting of two enzyme molecules and one tRNA molecule is first formed. It is subsequently dissociated to a one to one complex when more tRNA is present in the solution. The association curve shows a maximum for a molecular ratio, enzyme over tRNA, equal to 2.
The localization of the RNA in a spherical plant virus is established by neutron diffraction. For BMV, this localization is different at low pH than it is at high pH (swollen virus).
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