ROLE OF THE MITOCHONDRIAL DNAJ HOMOLOG, MDJ1P, IN THE PREVENTION OF HEAT-INDUCED PROTEIN AGGREGATION

The role of the mitochondrial Hsp70 system in the prevention of heat-i nduced protein aggregation was studied in isolated mitochondria from S accharomyces cerevisiae. Firefly luciferase was employed as a thermola bile tester protein. After shift to 40 degrees C a transient increase of mt-Hsp70 nuciferase complex was observed, which required functional Mdj1p and Mge1p, the mitochondrial homologues of DnaJ and GrpE. The k inetics of luciferase aggregation, however, were not influenced by mut ations in either mt-Hsp70 or Mge1p. Only the absence of Mdj1p led to e nhanced protein aggregation, Thus, a central role in the transient pro tection against heat stress is attributed to this mitochondrial DnaJ h omologue.