The effects of cycloheximide (CH) on the induction of β^major-globin mRNA by SB. Ba/F3 cells were exposed to SB and/or CH for the first or second 5-hour period according to the treatment schedules shown in the top of the figure. In panels 4 and 5, and in panels 7 and 8, SB was added back to the medium after cells were washed at 5 and 10 hours of the incubation period, respectively. RNA was extracted at 48 hours and subjected to northern hybridization (bottom of the figure). The cell densities at 48 hours are shown. The concentrations of SB and CH used were 1 mmol and 10 μmol/L, respectively. CH at this concentration inhibited protein synthesis, measured by incorporation of ³⁵S-methionine into the acid-insoluble fraction, by more than 95% (data not shown).