YEAST ACONITASE MITOCHONDRIAL IMPORT IS MODULATED BY INTERACTIONS OF ITS C AND N TERMINAL DOMAINS AND SSA1/2 (HSP70)

Molecules of single proteins, echoforms, can be distributed between two (or more) subcellular locations, a phenomenon which we refer to as dual targetingor dual localization. The yeast aconitase gene ACO1 (778 amino acids), encodes a single translation product that isnonethelessdual localized tothe cytosoland mitochondriaby areverse translocation mechanism. Thesolved crystal structure of aconitase isolated fromporcine heart mitochondria showsthat it has four domains. The first three tightly associatedN-terminal domains aretethered to the larger C-terminal fourth domain (C-terminal amino acids 517–778). We have previously shown that the aconitase C terminal domain constitutes an independent dual targeting signal when fused to mitochondria-targeted passenger-proteins. We show that the aconitase N and C-terminal domains interact and that this interaction is important for efficient aconitase post translational import into mitochondria and for aconitase dual targeting (relative levels of aconitase echoforms). Our results suggest a “chaperone-like function” of the C terminal domain towards the N terminal domains which can be modulated by Ssa1/2 (cytosolic Hsp70).