Disruption of the gene for Hsp30, an alpha-crystallin-related heat shock protein of Neurospora crassa, causes defects in import of proteins into mitochondria

The gene for Hsp30, the only known a-crystallin-related heat shock protein of Neurospora crassa, was disrupted by repeat-induced point mutagenesis, le ading to loss of cell survival at high temperature, Hsp30, which is not syn thesized at 30 degrees C, associates reversibly with the mitochondria at hi gh temperature (45 degrees C), In this study, we found that import of selec ted proteins into internal compartments of mitochondria, following their sy nthesis in the cytosol, was severely impaired at high temperature in a stra in mutant in Hsp30, After 70 min of cell incubation at 45 degrees C, most m atrix, inner membrane, and intermembrane-space proteins tested were reduced in import by about 50-70% in the mutant, as compared to wild-type cells, I n contrast, assembly of selected proteins into the outer mitochondrial memb rane was not reduced, except for one component of the preprotein translocas e complex of the mitochondrial outer membrane. Three proteins of this compl ex co-immunoprecipitated with Hsp30 of wild-type cells incubated at 45 degr ees C, We propose that Hsp30 interacts with the preprotein translocase of t he mitochondrial outer membrane and that it chaperones the activity of one or more components of this translocase complex at high temperature.