Biogenesis of mitochondrial porin

We review here the present knowledge about the pathway of import
and assembly of porin into mitochondria and compare it to those of
other mitochondrial proteins. Porin, like all outer mitochondrial
membrane proteins studied so far is made as a precursor without a
cleavble lsquosignalrsquo sequence; thus targeting information must
reside in the mature sequence. At least part of this information
appears to be located at the amino-terminal end of the molecule.
Transport into mitochondria can occur post-translationally. In a
first step, the porin precursor is specifically recognized on the
mitochondrial surface by a protease sensitive receptor. In a second
step, porin precursor inserts partially into the outer membrane.
This step is mediated by a component of the import machinery common
to the import pathways of precursor proteins destined for other
mitochondrial subcompartments. Finally, porin is assembled to
produce the functional oligomeric form of an integral membrane
protein wich is characterized by its extreme protease resistance.