Amino acid starvation boosts mitochondrial protein synthesis.

<p>(<b>A</b>) 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 <i>c</i> oxidase; ND1-6 and 4L, subunits of respiratory complex I; Cyt <i>b</i> – Cytochrome <i>b</i> of respiratory complex III; A6 and A8, subunits of ATP synthase. A section of the Coomassie blue-stained gel indicates equal protein loading. (<b>B</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). (<b>C</b>) 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 <i>t</i>-test, (P<0.05 *, P<0.01 **, and P<0.001 ***). (<b>D</b>) 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.