Spectroscopic evidence for the uneven distribution of adenine and uracil residues in ribosomal ribonucleic acid of Drosophila melanogaster and of Plasmodium knowlesi and its possible evolutionary significance

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Abstract
RNA was isolated from subribosomal particles of the malaria parasite P. knowlesi. The nucleotide composition (mol fraction) of the principal species was obtained (S-rRNA, 0.295A, 0.36U, 0.25G, 0.105C: L-rRNA, 0.326A, 0.31U, 0.228G, 0.144C). rRNA was also isolated from D. melanogaster. Optical properties of these A + U-rich species were measured. In all 4 cases analysis of the hypochromic effect revealed that adenine and uracil residues tended to form clusters along the polynucleotide chain. A substantial fraction of residues was located in bihelical regions of .apprx. 50% G .cntdot. C base pairs or in regions of .apprx. 30-35% G .cntdot. C base pairs. The possible evolutionary significance of these results was considered on the basis of comparison with properties of rRNA from bacteria (Escherichia coli) and a mammal (rabbit reticulocyte).