FIGURE 2.

Both ATF4 and CHOP mRNAs are preferentially associated with large polysomes during ER stress. Wild-type MEF cells were exposed to the ER stress agent thapsigargin for 6 h (stress) or no stress treatment. Cell lysates were then analyzed by centrifugation in a 10–50% sucrose gradient, and the profiles were measured by absorbance at 254 nm. The top panel highlights the 40 S and 60 S ribosomal subunits, 80 S monosomes, and polysomes. Total RNA was prepared from the fractions collected from the sucrose gradients, and the percentage of ATF4, CHOP, and actin-encoding transcripts present in each of the seven fractions derived from the ER stress (Stress) or the nontreated cells (No stress) were determined by qRT-PCR. Values are represented as histograms for each fraction. Three independent experiments were carried out for each measurement, with the S.D. indicated for each. The top panel is representative of three independent experiments.