Aep3p Stabilizes the Mitochondrial Bicistronic mRNA Encoding Subunits 6 and 8 of the H+-translocating ATP Synthase of Saccharomyces cerevisiae

Abstract

Subunits 6 and 8 of the mitochondrial ATPase in Saccharomyces cerevisiae are encoded by the mitochondrial genome and translated from bicistronic mRNAs containing both reading frames. The stability of the two major species of ATP8/6 mRNA, which differ in the length of the 5 -untranslated region, depends on the expression of several nuclear-encoded factors. In the present study, the product of the gene designated AEP3 (open reading frame YPL005W) is shown to be required for stabilization and/or processing of both ATP8/6 mRNA species. In an aep3-disruptant strain, the shorter ATP8/6 mRNA was undetectable, and the level of the longer mRNA was reduced to ϳ35% that of wild type. Localization of a hemagglutinin-tagged version of Aep3p showed that the protein is an extrinsic constituent of the mitochondrial inner membrane facing the matrix.

Human Mitochondrial mRNAs Are Stabilized with Polyadenylation Regulated by Mitochondria-specific Poly(A) Polymerase and Polynucleotide Phosphorylase

“…In yeast mitochondria, all mRNAs lack the poly(A) tail, and mt mRNAs are stabilized by mRNA-specific factors. For example, ATP8/6 mRNA requires four nuclear genes, NCA2, NCA3, NAM1, and AEP3, for its stabilization (12,(41)(42)(43)(44). Although no human homolog of these yeast genes has been identified, it can be speculated that the mRNA-specific protein factor(s) with similar function might be involved in the stabilization of human ND3 mRNA.…”

“…In yeast mitochondria, mRNAs lack the poly(A) tail, and mt gene expression seems to be regulated by the mtDNA-encoded conserved dodecamer sequence at its 3Ј terminus (11). It is known that the stability of yeast mitochondrial (mt) mRNA is controlled by mRNA-binding proteins (12)(13)(14). In trypanosome mitochondria, the length of the poly(A) tail is dependent on the edited status of the mRNA (15)(16)(17).…”

The Saccharomyces cerevisiae ATP22 Gene Codes for the Mitochondrial ATPase Subunit 6-Specific Translation Factor

“…Western analysis of ATPase subunits indicated that atp22 point mutants are grossly deficient in subunit 6 (Helfenbein et al 2003). A subunit 6 deficit is not necessarily related to translation of the protein or absence of the mRNA (Ellis et al 2004) but can also be caused by its turnover in mutants defective in F 0 assembly (Paul et al 1989(Paul et al , 2000Arselin et al 1996). In our earlier studies of the atp22 mutant, N417, some incorporation of 35 S-methionine into subunit 6 was observed when cells were labeled in vivo in the presence of cycloheximide to arrest cytoplasmic protein synthesis (Helfenbein et al 2003).…”

“…Mutations in NCA2 and NCA3 when present in the same strain produce an increased ratio of the 4.6-kb relative to the 5.2-kb transcript and decreased translation of subunits 6 and 8 Pelissier et al 1995). Mutations in AEP3 render the ATP6/ATP8/ENS2 transcripts unstable (Ellis et al 2004). Northern analysis of ATP6 transcripts in an atp22 point mutant indicates the presence of both the 4.6-and the 5.2-kb transcripts, although processing of the larger 5.2-to the 4.6-kb transcript is less efficient than in wild type.…”

“…The other nine genes affect expression of the F 0 unit of the ATPase. Their products target the mitochondrially encoded subunits 6 and 9 of F 0 by promoting processing, stability, and translation of the mRNAs (Payne et al 1991;Camougrand et al 1995;Paul et al 2000;Helfenbein et al 2003;Ellis et al 2004). One such protein, encoded by ATP22 and located in the inner membrane of mitochondria, was shown to be necessary for expression of F 0 (Helfenbein et al 2003).…”