Properties and mechanism of synthesis of ribosomal RNA in evolution.

The molecular weights, base compositions and nucleotide sequences of ribosomal RNA show differences which can be systematically related to the major phyla of plants and animals. The ribosomal RNA precursor, which is the direct product of the ribosomal genes in the nucleolus, has diverged more than the mature RNA; the differences are in the excess RNA which is degraded during maturation; the warm-blooded animals have at least twice as much of this excess RNA as any other species.