ROLE OF THE N-TERMINI AND C-TERMINI OF PORIN IN IMPORT INTO THE OUTER-MEMBRANE OF NEUROSPORA MITOCHONDRIA

The signals for targeting and assembly of porin, a protein of the mito chondrial outer membrane, have not been clearly defined, Targeting inf ormation has been hypothesized to be contained in the N-terminus, whic h may form an amphipathic alpha-helix, and in the C-terminal portion o f the protein, Here, the role of the extreme N- and C-termini of porin from Neurospora crassa in its import into the mitochondrial outer mem brane was investigated, Deletion mutants mere constructed which lacked the N-terminal 12 or 20 residues or the C-terminal 15 residues. The p orins truncated at their N-termini mere imported in a receptor-depende nt manner into the outer membrane of isolated mitochondria, When integ rated into the outer membrane, these preproteins displayed an increase d sensitivity to protease as compared to mild-type porin, In contrast, mutant porin truncated at its C-terminus did not acquire protease res istance upon incubation with mitochondria. Thus, unlike most other mit ochondrial preproteins, porin appears to contain important targeting a nd/or assembly information at its C-terminus, rather than at the N-ter minus.