Structural Comparison of 26S and 17S Ribosomal RNA of Yeast

THE two large ribosomal RNA components (26S and 17S rRNA) of yeast exhibit a noteworthy structural similarity as judged by nucleotide composition 1 , the degree of methylation 2 , and the extensive cross hybridization with homologous DNA 3 . Because the 17S rRNA can compete with much more than 50 per cent of 26S rRNA in hybridization with homologous DNA 3 , and because the estimated chain length of the 26S rRNA is about twice that of 17S rRNA (ref. 4 and R. C. v. d. B., J. Retèl and R. J. P., manuscript in preparation), it seems reasonable to assume that the 26S rRNA comprises two segments, each showing some similarity to a 17S rRNA molecule. But although competition in hybridization with DNA does mean that the two RNA species exhibit some primary structural homology, it certainly does not indicate that they have identical base sequences.