Ribosome subunit to polysome ratios affect the synthesis of rRNA in Drosophila cells

Abstract

Many investigations have revealed that ribosome numbers increase in parallel with the growth rate of cells. Here we show that the absolute level of protein synthesis may not be the only factor influencing rRNA synthesis in a nondividing eukaryotic cell. Under conditions of complete (greater than 99%) inhibition of protein synthesis by four different antibiotics, there is a corresponding inhibition of rRNA synthesis. At lower levels of inhibition of protein synthesis (70%), a different effect of individual antibiotics on rRNA synthesis is observed. Cycloheximide and anisomycin, which cause a decrease in the free subunit pool due to a buildup of polysomes, stimulate rRNA synthesis, whereas puromycin and pactamycin, which cause an increase in the free subunit pool, cause a decrease in rRNA synthesis. These effects on rRNA synthesis are not solely due to a low level of completed proteins. Pactamycin treatment allows completed proteins to be made yet lowers rRNA labeling, while anisomycin treatment does not show synthesis of complete proteins yet increases rRNA labeling. The result suggest that eukaryotic cells may regulate ribosome synthesis in response to the number of free versus translating (polysomal) ribosomes as do Escherichia coli cells.

Disruption of Persistent Nociceptive Behavior in Rats with Learning Impairment

“…Cycloheximide has been shown to inhibit protein synthesis in brain homogenates [35–37] and disrupt learning and memory when administered to chicks in conjunction with a reminder treatment [38]. The effect of cycloheximide on learning and memory consolidation is likely due to its role in blocking translation of polypeptide chains at the elongation and termination phases and provoking the accumulation of ribosome subunits on mRNA leading to inhibition of the protein synthesis [39]. In this experiment, disruption of learning and memory was independently confirmed by the Morris water maze task in rats receiving cycloheximide, but not vehicle, injection into bilateral hippocampal CA1 area, which lasted for at least 19 days after the cycloheximide treatment.…”