This is the N-terminal region of the E or R chain, Ubiquitinol-cytochrome C reductase Fe-S subunit, of the hetero-hexameric cytochrome bc1 complex. This region is a TAT-signal region. The cytochrome bc1 complex is an oligomeric membrane protein complex that is a component of respiratory and photosynthetic electron transfer chains. The enzyme couples the transfer of electrons from ubiquinol to cytochrome c with the the generation of a protein gradient across the membrane [1]. The motif is also associated with Rieske (Pfam:PF00355), UCR_TM (Pfam:PF02921) and Ubiq-Cytc-red_N (Pfam:PF09165).

1: Structure at 2.3 A resolution of the cytochrome bc(1) complex from the yeast Saccharomyces cerevisiae co-crystallized with an antibody Fv fragment. Hunte C, Koepke J, Lange C, Rossmanith T, Michel H; Structure. 2000;8:669-684. PMID:10873857