70-kD heat shock-related protein is one of at least two distinct cytosolic factors stimulating protein import into mitochondria.

TLDR

We have developed an in vitro system in which posttranslational import of the mitochondrial matrix enzyme Put2 into yeast mitochondria requires addition of yeast postribosomal supernatant (PRS). The addition of PRS, which contains at least two synergistic factors—a 70‑kD heat shock‑related protein (Ssalp/Ssa2p) and an N‑ethylmaleimide‑sensitive protein—dramatically enhances posttranslational import of Put2 into yeast mitochondria.

Abstract

We have developed an in vitro system in which the posttranslational import of Put2 (delta-pyrroline-5-carboxylate dehydrogenase), into yeast mitochondria is dependent on the addition of yeast postribosomal supernatant (PRS). When mRNA for a nuclear-encoded yeast mitochondrial matrix protein, Put2, was translated in a wheat germ cell-free system, import into posttranslationally added yeast mitochondria was negligible. However, when a yeast PRS was added, significant import was observed. The import stimulating activity of the yeast PRS was shown to consist of at least two distinct factors. One of these is the recently purified 70-kD heat shock-related protein Ssalp/Ssa2p, two proteins that are 98% homologous. The other factor is an N-ethylmaleimide-sensitive protein(s). Both factors act synergistically.