Splicing before import - An intein in a mitochondrially targeted preprotein folds and is catalytically active in the cytoplasm in vivo

Nuclear-encoded mitochondrial proteins are cytoplasmically synthesized and imported into the organelle. The intein-containing RecA protein of Mycobact erium tuberculosis, with or without the CoxIVp mitochondrial targeting sign al (MTS), was used to determine where a protein targeted to mitochondria fo lds and becomes catalytically active. Analysis of fractions from Saccharomy ces cerevisiae cells expressing RecA without the MTS revealed that RecA and intein proteins remained cytoplasmic, With the MTS, most of RecA was direc ted to mitochondria, while most of the intein remained in the cytoplasm, Th e intein therefore folds into a catalytically active state in the cytoplasm prior to RecA import into mitochondria. (C) 2000 Federation of European Bi ochemical Societies. Published by Elsevier Science B.V. All rights reserved .