Focus on cellular biochemistry - Mechanisms of mitochondrial protein import

Import of nuclear encoded precursor proteins into and across the mitochondr ial inner membrane is mediated by two distinct translocases, the TIM23 comp lex and the TIM22 complex, which both cooperate with the general preprotein translocase of the outer membrane, TOM complex. The TIM23 complex mediates import of preproteins with a positively charged matrix-targeting signal, w hile the TIM22 complex mediates the import of a class of integral inner-mem brane proteins which do not carry a matrix-targeting signal. The focus of t his review is on the structural organization and function of components tha t act along these import pathways and their conservation between species.