Figure 4.

Synthesis of plastid-encoded PSI subunits is not reduced in psa3 mutants. A, In vivo pulse-chase analysis of chloroplast-encoded thylakoid membrane proteins. The leaves of 12-d-old Arabidopsis seedlings were preincubated with cycloheximide for 30 min, and [³⁵S]-Met was then added for 20 min (t = 0). Unlabeled Met was then added to a concentration of 1 mm (chase) and plants were harvest 1 and 2 h later. A crude membrane fraction (30,000 cpm) was resolved by SDS-PAGE and imaged with a phosphorimager. B, Summary of ribosome profiling data for PSI-related chloroplast mRNAs in Zm-psa3 mutants. Ribosome footprints were quantified by hybridization to high-resolution microarrays as in Zoschke et al. (2013). The values shown are the average normalized signal intensities among all 50-nt array probes mapping within each gene, in two replicate experiments. These values reflect the average ribosome density (average ribosome abundance per 50 nt) for each gene. A genome-wide view of the data are shown in Supplemental Figure S5A.