Effects of Valine Deprivation on the Biosynthesis of Ribosomal and Messenger RNA in a Mammalian Cell Line (L 5178 Y)

It has been well demonstrated in bacteria that RNA syntheses are non‐coordinated. In order to study this problem in mammals, qualitative and quantitative studies of rRNA, polysomal mRNA, and RNA of heterogeneous ribonucleoproteic particles syntheses have been performed, during exponential growth and valine starvation. During the latter, the residual synthesis of these three classes of RNA were respectively calculated as 38, 70 and 90% of the control. Whatever is the physiological significance of these particles one can conclude that the RNA syntheses in mammals are not coordinated. This result resembles those observed in stringent bacteria strains. In addition, the “45 S fraction” isolated from sucrose gradient appears to be heterogeneous in CsCl gradient. This could be interpreted by the existence of several classes of particles, heterogeneous ribonucleoproteic particles and small ribosomal subunits more or less mature. Finally, some heterogeneous ribonucleoproteic particles with high density (ϱ= 1.60 g/cm 3) were found. This is not in complete accordance with the generally finding, that these particles are characterized by a low density.