Fig. 6. Specific phosphorylation as a function of translation rate. (A) Elongation was reduced by incubation of transfected COS-1 cells with different concentrations of cycloheximide during 40 min of [³⁵S]methionine labeling. Saponin extraction, immunoprecipitation and fluorography were then performed. (B and C) COS-1 cells expressing H1rev20-P_N or H1rev85-P_N were labeled with [³⁵S]methionine and [³²P]phosphate, saponin extracted, immunoprecipitated and analyzed by gel electrophoresis. The specific phosphorylation (average with standard deviation from three determinations each) normalized to that determined in the absence of inhibitor is plotted against the relative translation time of the N-terminal domain from the emergence of the phosphorylation tag to the appearance of a minimal signal (translation of 30 and 95 residues, respectively). The lower scale provides absolute times of translation for a translation rate of 5 amino acids/s.