Synthesis of proteins and RNA of the 60S ribosomal subunit in HeLa cells recovering from valine deprivation.

The synthesis of ribosomes in HeLa cells was studied during recovery from a 20-hour deprivation for valine. The rates of incorporation of labeled precursors into ribosomal pre-RNA, processed rRNA, total cellular proteins, and proteins of the 60S ribosomal subunit returned to normal or nearly normal levels immediately after restoration of valine to the medium. Specific proteins of the 60S ribosomal subunit, whose apparent net synthesis is reduced more than that of the other proteins of the 60S ribosomal subunit during valine deprivation, were no longer undersynthesized after valine was restored. This rapid recovery suggests that the apparent decrease in the net rate of synthesis of these ribosomal proteins during valine deprivation is effected at the translational or post-translational level. No evidence of significant synchrony in any particular stage of the cell cycle was observed after a 20-hr valine deprivation.