ISOLATION OF A CDNA CLONE SPECIFYING RAT CHAPERONIN-10, A STRESS-INDUCIBLE MITOCHONDRIAL MATRIX PROTEIN SYNTHESIZED WITHOUT A CLEAVABLE PRESEQUENCE

We have isolated a cDNA clone encoding chaperonin 10 from rat liver Th e cDNA specifies a protein of 102 amino acids which, when transcribed and translated in vitro, yields a single basic product (pI > 9) that c o-migrates exactly with the heat shock inducible cpn10 of rat hepatoma cells during 2D gel-electrophoresis. It is concluded that cpn10, unli ke the majority of nuclear-encoded proteins of the mitochondrial matri x, is synthesised without a cleavable targeting signal and that, follo wing removal of the initiating methionine, it becomes acetylated prior to mitochondrial import. Incubation of H-3- or S-35-labelled cpn10 wi th mitochondria confirms these conclusions and shows that cpn 10 is im ported into mitochondria in an energy-dependent process which is inhib ited by the presence of 2,4-dinitrophenol.