The in vitro and in vivo inactivation of ribosomes by virginiamycin M does not entail an alteration of 5, 16 and 23 S ribosomal RNA.

The M component of virginiamycin blocks protein synthesis by inactivating catalytically the 50 S ribosomal subunits: the in vitro interaction of 50 S with virginiamycin M, followed by removal of the antibiotic, results in a lasting damage of the particle. This enzyme-like inactivation of 50 S subunits resembles that of 30 S subunits by colicin E3, which entails the cleavage of 16 S rRNA. To explore this possibility, rRNA obtained from particles incubated in vivo and in vitro with virginiamycin M were analyzed. Electrophoretic analysis of 5, 16 and 23 S rRNA did not reveal major changes, nor did it show the appearance of additional fragments. To exclude the possibility of terminal alterations, the 5'- and 3'-extremities of these RNA were also sequenced and found unchanged. Conclusions drawn in the present work parallel those of an accompanying paper (Moureau, P., Di Giambattista, M. and Cocito, C. (1983) Biochim. Biophys. Acta 739, 164-172) describing the dissociation and reassociation of ribosomes incubated with virginiamycin M: the lasting ribosome damage by this antibiotic appears to be due to a conformational rather than to a structural alteration.