EFFECTS OF VALINE DEPRIVATION ON RIBOSOME FORMATION IN HELA CELLS

When HeLa cells are deprived of the essential amino acid, valine, the formation of new ribosomes continues at a reduced rate compared to growing cells. Examination of nucleolar RNA reveals that during valine starvation there is a considerable decrease in the rate of 45 s ribosomal precursor RNA synthesis and of its conversion into 32 s RNA. Restoration of valine reverses these effects, but cycloheximide prevents reversal. The total steady-state level of nucleolar RNA remains practically constant for many hours after the onset of valine deprivation, but small changes in the relative amounts of 45 s and 32 s RNA occur. Preliminary experiments on cells deprived of other amino acids give results similar to those observed during valine deprivation. The findings indicate that in HeLa cells the availability of some particular protein or proteins may regulate the rate of synthesis and cleavage of ribosomal precursor RNA. © 1969.