EFFECT OF TOYOCAMYCIN ON CELLULAR RNA SYNTHESIS

Small concentrations of the adenosine analogue toyocamycin inhibit the maturation of rRNA, but permit the synthesis of other cellular RNA species including 45-S RNA. This hypothesis is supported by the following evidence: 1. 1. The base composition of the 45-S RNA, which accumulates in the nucleoli in the presence of toyocamycin, is the same as that of natural precursor 45-S RNA. 2. 2. Despite the fact that rRNA is not synthesized in the presence of toyocamycin, some de novo synthesized RNA was bound in the cell to the polyribosomes. An analysis of this RNA revealed properties characteristic of mRNA including intracellular localization, extreme sensitivity toward ribonuclease, base composition, and a correspondence between the size of a given class of polyribosomes and the sedimentation constant of the de novo RNA bound to it. 3. 3. 5-S RNA was synthesized in the course of toyocamycin treatment. The de novo 5-S RNA was not associated with ribosomes. 4. 4. We reported previously that the synthesis of tRNA was uninhibited by toyocamycin. © 1969.