Mictochondria

Mitochondria

Molecular Insights into Intracellular RNA LocalizationMichael D. Blower, in International Review of Cell and Molecular Biology, 20132.2 MitochondriaMitochondria are the cellular sites of respiration, energy production and some aspects of calcium handling. Mitochondria are unique organelles as they contain a fraction of the genetic information required for their maintenance, and must also import many proteins that are encoded by nuclear DNA (Ernster and Schatz, 1981). Import of proteins into the mitochondria was thought to occur posttranslationally as proteins translated in vitro are capable of import into the mitochondria (Neupert and Herrmann, 2007). However, ribosomes are present on the surface of yeast mitochondria, suggesting that there may be co-translational import of some proteins into the mitochondria (Kellems et al., 1974, 1975). Genome-wide studies of purified yeast mitochondria have demonstrated that several hundred mRNAs copurify with mitochondria-bound ribosomes (Gadir et al., 2011; Saint-Georges et al., 2008). Interestingly, the majority of the mitochondria-localized mRNAs code for proteins that function in the mitochondria, consistent with a role for co-translational protein import. Localization of a subset of these mitochondria-localized mRNAs has revealed that translation of the N-terminal mitochondrial targeting sequence (MTS), as well as specific RNA elements both in the coding regions and 3′UTRs are important for mRNA targeting to mitochondria (Corral-Debrinski et al., 2000).Globally, the majority of mitochondria-localized transcripts depend on translation to target to the mitochondria, but as is the case with the ER, there is a class of mRNAs that localize independently of translation (Saint-Georges et al., 2008). Two studies have shown the Puf3 RNA-binding protein is important for localization of a subset of transcripts to the mitochondria: Puf3 associates primarily with transcripts that function at the mitochondria (Gerber et al., 2004) and is required for the localization of these transcripts to the organelle (Gadir et al., 2011; Saint-Georges et al., 2008). Interestingly, deletion of mitochondria-targeting elements within the ATP2 mRNA resulted in defects in mitochondrial respiration and defects in protein import into the mitochondria, demonstrating that mRNA localization to mitochondria is critical for the proper function of the organelle (Margeot et al., 2002). In addition, a recent study of in Xenopus cultured neurons identified a nuclear protein, Lamin B2, as being translated in the axon. Surprisingly, the axonal pool of translated LB2 protein localized to mitochondria where it was required for proper mitochondrial function (Yoon et al., 2012). It will be interesting to determine how some messages localize independently of translation and what role those messages play in mitochondrial function.



Michael D. Blower, in International Review of Cell and Molecular Biology, 20132.2 MitochondriaMitochondria are the cellular sites of respiration, energy production and some aspects of calcium handling. Mitochondria are unique organelles as they contain a fraction of the genetic information required for their maintenance, and must also import many proteins that are encoded by nuclear DNA (Ernster and Schatz, 1981). Import of proteins into the mitochondria was thought to occur posttranslationally as proteins translated in vitro are capable of import into the mitochondria (Neupert and Herrmann, 2007). However, ribosomes are present on the surface of yeast mitochondria, suggesting that there may be co-translational import of some proteins into the mitochondria (Kellems et al., 1974, 1975). Genome-wide studies of purified yeast mitochondria have demonstrated that several hundred mRNAs copurify with mitochondria-bound ribosomes (Gadir et al., 2011; Saint-Georges et al., 2008). Interestingly, the majority of the mitochondria-localized mRNAs code for proteins that function in the mitochondria, consistent with a role for co-translational protein import. Localization of a subset of these mitochondria-localized mRNAs has revealed that translation of the N-terminal mitochondrial targeting sequence (MTS), as well as specific RNA elements both in the coding regions and 3′UTRs are important for mRNA targeting to mitochondria (Corral-Debrinski et al., 2000).Globally, the majority of mitochondria-localized transcripts depend on translation to target to the mitochondria, but as is the case with the ER, there is a class of mRNAs that localize independently of translation (Saint-Georges et al., 2008). Two studies have shown the Puf3 RNA-binding protein is important for localization of a subset of transcripts to the mitochondria: Puf3 associates primarily with transcripts that function at the mitochondria (Gerber et al., 2004) and is required for the localization of these transcripts to the organelle (Gadir et al., 2011; Saint-Georges et al., 2008). Interestingly, deletion of mitochondria-targeting elements within the ATP2 mRNA resulted in defects in mitochondrial respiration and defects in protein import into the mitochondria, demonstrating that mRNA localization to mitochondria is critical for the proper function of the organelle (Margeot et al., 2002). In addition, a recent study of in Xenopus cultured neurons identified a nuclear protein, Lamin B2, as being translated in the axon. Surprisingly, the axonal pool of translated LB2 protein localized to mitochondria where it was required for proper mitochondrial function (Yoon et al., 2012). It will be interesting to determine how some messages localize independently of translation and what role those messages play in mitochondrial function.