Mitochondrial import inner membrane translocase subunit Tim21 (TIMM21)

Participates in the translocation of transit peptide- containing proteins across the mitochondrial inner membrane. Also necessary for assembly of mitochondrial respiratory chain complex I and complex IV as part of this MITRAC (mitochondrial translation regulation assembly intermediate of cytochrome c oxidase complex) complicated.

Probably shuttles between the presequence translocase and respiratory-chain assembly intermediates in a process which promotes incorporation of ancient nuclear-encoded subunits into these complexes. .