Circular dichroism studies on Mengo virus variants and their constituent ribonucleates

A comparison of the circular dichroic spectra of three variants of Mengo virus and their constituent ribonucleates shows that the curves are essentially identical to one another, with respect to crossover points and the positions and amplitudes of troughs and peaks. This would suggest that the manner in which the proteins are arranged around the RNA chain in the virus is precise and similar in all three cases, and that there are no significant differences in the density of packing among the virions. By subtracting the RNA contribution from that of the virus, the circular dichroic curve of the protein in situ was obtained. The small amplitude of the ellipticity bands at ~205 and 220 mμ (transitions characteristic of the right-handed α-helix) suggests that the protein, as it exists in the virion, possesses a low α-helical content. This observation is consistent with the fact that the viral protein contains a large content of proline and non-α-helix-forming amino acids.

Ultraviolet circular dichroism studies on complexes of synthetic polynucleotides

The ultraviolet circular dichroism spectra of complexes of polyadenylic acid and polyuridylic acid in the molar ratio of 1:1 and 1:2, and that of polyguanylic acid and polycytidilic acid have been examined over the wavelength range of 300–185 mμ. Increased resolution of spectra below 225 mμ has revealed several new ellipticity bands for these complexes which should be of considerable value in the proper counting of optically active electronic transitions and their assignment in these systems, and with naturally occurring RNA's.

Ultraviolet circular dichroism studies on synthetic polynucleotides

The ultraviolet circular dichroism spectra of polyadenylic acid, polyguanylic acid, polycytidylic acid, polyinosinic acid, and polyuridylic acid have been examined at neutral and acidic pH values, and at moderate and low ionic strengths, over the wavelength range 300–185 mμ. Increased resolution of spectra below 225 mμ has revealed heretofore unexamined ellipticity bands in the low wavelength region, which are sensitive to conformational alterations for those polynucleotides which exhibit both single and multistranded secondary structures. It is concluded that these ellipticity bands, in view of their extreme sensitivity to conformation, will be of significance in increasing the usefulness of the homopolynucleotides as model compounds in conformational studies of naturally occurring RNAs.

Optical rotatory dispersion and absorbance-temperature studies on wheat embryo ribosomal ribonucleates

Wheat embryo ribosomal RNA (rRNA) has been shown by optical rotatory dispersion (o.r.d.) and absorption–temperature measurements to possess a substantial secondary structure in solution which is stabilized by hydrogen bonding of paired bases in helical segments, and by nearest-neighbor base stacking in single-stranded segments of the molecule. Experimental conditions were established where single-strand stacked conformations predominated over base-paired regions. This state of affairs was effected by reducing the number of hydrogen-bonded nucleotides in RNA by any of three treatments: protonation, formylation, or reduction of the ionic strength of the medium to essentially zero. At the same time, use of the organic solvent ethylene glycol, which preferentially breaks hydrophobic bonds, has demonstrated that base stacking plays a significant role, as well, in the stabilization of the native conformation. Application of the empirical method of C. R. Cantor, S. R. Jaskunis, and I. Tinoco (J, Mol. Biol. 20, 39 (1966)), whereby it is possible to predict the optical rotatory properties of single-stranded polynucleotides from the corresponding properties of oligonucleotides, successfully demonstrated that wheat embryo rRNA, in the absence of salt, is predominantly in a single-stranded stacked conformation. From hyperchromicity data measured on RNA under conditions where hydrogen-bonding and base-stacking forces were delineated, the helical content of wheat embryo rRNA has been estimated as 65%. In view of the close similarity in the o.r.d. curves of RNA in salt solution and in the ribosome, it is concluded that RNA in the ribosome must be in a largely base-paired double-helical conformation, joined by single-stranded links.

Cri du chat syndrome

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