Amino Acid Starvation Has Opposite Effects on Mitochondrial and Cytosolic Protein Synthesis
Figure 2
Amino acid starvation boosts mitochondrial protein synthesis.
(A) One-hour 35S-methionine pulse-labeling of nascent mitochondrial polypeptides in HEK cells grown for 72 h in different media (see Figure legend 1), and fractionated by 12% SDS-PAGE. Tentative assignments of the mitochondrial polypeptides are indicated to the left of the gel: COI-III, subunits of cytochrome c oxidase; ND1-6 and 4L, subunits of respiratory complex I; Cyt b – Cytochrome b of respiratory complex III; A6 and A8, subunits of ATP synthase. A section of the Coomassie blue-stained gel indicates equal protein loading. (B) Pulse-labelings of nascent mitochondrial polypeptides and fractionation as per panel A except that the labeling medium lacked all amino acids (other than 35S-methionine). (C) The combined signal of the labeled mitochondrial proteins was quantified and normalized with respect to HG+AA. HG, n = 6 experiments; LG, n = 3 experiments; and Gal, n = 3 experiments. The error bars represent the s.e.m.; unpaired student’s t-test, (P<0.05 *, P<0.01 **, and P<0.001 ***). (D) The growth rates of cells grown in HG with or without AA were monitored and measured over the course of 7 days. Broken vertical lines at 6, 26, and 72 h indicate the times at which the mitochondrial translation capacity was measured.