tRNAs and strongly reduced mitochondrial translation, FAS 2 mutants have a pleiotropic phenotype. A membrane-attached form of mt-RNase P? Previous publications suggest that yeast mt-RNase P is difﬁcult to purify without the aid of detergents (16–18), and at least partially membrane-bound. Unfortunately, measuring mt-RNase P activity of mitochondrial membrane fractions is difﬁcult because of rapid unspeciﬁc degradation of the pre-tRNA. We have therefore tracked mt-RNase P quantities by localization of its known GFP-labeled protein subunit (Rpm2p), and ﬁnd that 54% of GFP-Rpm2p is in the soluble mitochondria matrix fraction. With a mild detergent (1% digitonin) the amount of soluble GFP-Rpm2p increases to only 68%, suggesting that the RMT complex has indeed a strong tendency for membrane attachment, but we clearly conﬁrm that more than half is soluble, integrated with the RMT complex. CONCLUSION Here we show that native mt-RNase P and RNase Z activities are organized in a stable RMT supercomplex in yeast mitochondria, associated with the RNA degradosome, other RNA processing activities and several other mitochondrial functions including fatty acid synthesis, the complete TCA cycle and components of the translation machinery including a ribosome with both rRNAs but a reduced set of ribosomal proteins. Our results rationalize and further extend the surprising ﬁnding by others, that a deﬁciency in any component of the fatty acid type II biosynthetic pathway leads to impaired tRNA processing (24), and that deletion of genes coding for components of the RNA degradosome lead to pleiotropic defects in RNA processing and protein translation (33,34). 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