On the Conformation of Serine-Specific Transfer RNA. Studies by Small-Angle X-Ray Scattering and Ultraviolet Absorption of the Molecule in Solution

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Abstract
The scattered X-ray intensities from dilute solutions of tRNASer (baker''s yeast) in 0.1 M Soerensen buffer at pH 7.0 were measured at 25.degree. C. The radius of gyration, MW and volume were determined. A model equivalent in scattering is given. The change of the conformation of tRNASer by heating was followed by small-angle X-ray measurements and UV absorption in a temperature range 20-70.degree. C. The molecule begins to unfold at about 40.degree. C and at 70.degree. C has a random coil conformation. Addition of Mg stabilizes the tRNASer molecule. The reversibility of the melting process was studied by both methods. An interesting effect was found by UV absorption: by heating the tRNASer solutions to 55 and 60.degree. C and subsequently slowly cooling, the melting curves lie at higher absorption values than the corresponding cooling curves. The small-angle data and optical properties of tRNASer are compared those of tRNAPhe which was already thoroughly investigated.