Reference: Lee C, et al. (2009) Yeast AEP3p is an accessory factor in initiation of mitochondrial translation. J Biol Chem 284(49):34116-25

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Abstract


Initiation of protein synthesis in mitochondria and chloroplasts normally uses a formylated initiator methionyl-tRNA (fMet-tRNAfMet). However, mitochondrial protein synthesis in Saccharomyces cerevisiae can initiate with nonformylated Met-tRNAfMet, as demonstrated in yeast mutants in which the nuclear gene encoding mitochondrial methionyl-tRNA formyltransferase (FMT1) has been deleted. The role of formylation of the initiator tRNA is not known, but in vitro, formylation increases binding of Met-tRNAfMet to translation initiation factor 2 (IF2). We hypothesize the existence of an accessory factor that assists mitochondrial IF2 (mIF2) in utilizing unformylated Met-tRNAfMet. This accessory factor might be unnecessary when formylated Met-tRNAfMet is present, but becomes essential when only the unformylated species is available. Using a synthetic petite genetic screen in yeast, we identified a mutation in the AEP3 gene that caused a synthetic respiratory defective phenotype together with fmt1. The same aep3 mutation also caused a synthetic respiratory defect in cells lacking formylated Met-tRNAfMet due to loss of the MIS1 gene which encodes the mitochondrial C1-THF synthase. The AEP3 gene encodes a peripheral mitochondrial inner membrane protein that stabilizes mitochondrially encoded ATP6/8 mRNA. Here we show that the AEP3 protein (Aep3p) physically interacts with yeast mIF2, both in vitro and in vivo, and promotes the binding of unformylated initiator tRNA to ymIF2. We propose that Aep3p functions as an accessory initiation factor in mitochondrial protein synthesis.

Reference Type
Journal Article
Authors
Lee C, Tibbetts AS, Kramer G, Appling DR
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