Figure 6.

Mitochondrial protein biogenesis is compromised under heat stress. A, in organello translation of mitochondria-encoded proteins. Isolated mitochondria were heat-stressed as indicated, and the newly translated proteins were labeled with [³⁵S]Met/Cys. Samples were treated with cycloheximide and chloramphenicol to impede cytosolic or mitochondrial translation. Left panel, bands representing mitochondria-encoded subunits are indicated. ND, NADH dehydrogenase; CO, cytochrome c oxidase; A, ATP-synthase; Cyt b, cytochrome bc₁ complex. B, quantitative analysis of in organello translation reactions as described in A. Shown are mean relative values and S.E. of total incorporated radioactivity (n = 3; control values at 25 °C were set to 100%). C, mitochondrial protein import after heat stress. In vitro import of [³⁵S]Met/Cys-labeled preprotein Su9(70)DHFR into isolated intact mitochondria after heat stress preincubation as indicated. Where indicated, the inner membrane potential (Δψ) was depleted. Nonimported preproteins were digested by incubation with PK. Translated or imported proteins were analyzed by SDS–PAGE and detected by digital autoradiography. p, precursor; m, mature protein.