Abstract
When Paramecium tetraurelia in log phase growth is treated with 4% dimethyl sulphoxide (DMSO) for five minutes the amount of polyribosomes is reduced 3β to 4βfold while there is a corresponding increase in 80s ribosomal material. Reducing the concentration of DMSO to 1% allows immediate reversal of the condition.
Paramecium polyribosomes subjected to 4% DMSO either in whole cell homogenates or during purification through sucrose density gradients appear unaffected while cycloheximide at concentrations up to 100 ΞΌg/ml did not prevent DMSO from exerting its effect in vivo.
Analyses of ^14^C amino acid incorporation experiments indicated a strict correspondence between the effect of DMSO on polyribosomes and overall protein synthesis. The reduction of acid precipitable radioactivity in the polyribosomal region after DMSO treatment was associated with a corresponding increase in radioactivity in the 80s region. There was no comparable increase in the acid precipitable radioactivity in the soluble fraction.
The overall results of the study suggest that DMSO acts on polyribosomes indirectly through some unknown primary reaction with cell constituents, and that the mode of action is such as to cause the release of ribosomes from messenger RNA (mRNA) rather than to prevent initiation of the ribosomeβmRNA complex. Our data suggest that the effect may be selective.
Finally, it is of interest that high concentrations of DMSO (above 8%) appear to have the opposite effect of lower concentrations of DMSO, i.e., they appear to βfreezeβ the ribosomes to mRNA.