- Email: [email protected]
A reply to Preiss et al.
2 Capakdi,
ff.
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569-596 osle, M., Willter. M. and . (f988) EM50 J. :,2387-2391 N. et ai. (1990) J. 5ol. Chem. 265,2677-2681 5 Seelan, R. S. and Grossman, L. I. (1991) J. Bid. Chem. 266,19?52-19757 6 Preiss, T. and Lightowlers. R. N. (1993) J. Bal. C/x%?. 268,1@659-10667 7 Preiss, T., Hall, A. and Lightowlers, R. N. (1993) J. 43i~I. Chem. 268.24523-24526 8 Preiss, T., Sang, A. E., Chrzanowska-Lightowlers, Z. R/d.A. and Lightowlers, R. N. (1995) E5S Lert. 367,
In the recent Taking Point ‘Highways for protein delivery to the mitochondria’l Lithgow et al. raised the interesting possibility that intracellular mRNA localisation may play a role in facilitating protein transport to organelles such as the mitochondrion. Furthermore, it was ted that unidentified binding factors in the mitochondrial outer membrane may function to anchor selective mRNA species at the periphery of the organelle to aid in the co-translational tra~slocat~o~ of some mitochondria! preproteins. We wish to report a candidate for sue mRNA-binding factor, the mammalian mitochondrial enzyme g!utamate dehydrogenase. In addition to the three large subunits that are encoded by the mitochondrial genome, mammalian cytochrome c ox!dase (COx> is composed of numerous nuclear-encoded polypeptides, several of which are present as tissue-specific !soforms2. These nuclear-encoded isoforms are reported to be regulate the level of mRNA express!onR-5.In an attempt to discover whether this regulation was mediated by an
Nistochem. Cyt~~~em. 34,9%3-922
ral possible mechanisms for analattion of mitoct~ondr~~l mitochondrla would be the presence of an~ll~~pecific rn~A-bindin protein attached to the mltochon outer membrane’. Preiss et al. suggest that the enzyme glutamate dehydrogenase
Lightowlers, R. N. (1995) 291-296 and Schatz, G. (1995) ~~~~ J. 14. 239_3-2297
ase selectivity in the RNAsubstrates with which it can interact in uitd3.
in ~‘0 is its location within the mitoc~!ondrial matrix: in intact cells the protein IS separated from any mR!VA substrate by the two mitochondrial membranes. While it remains a formal possibility that glutamate dehydrogenase might actually cross both mitochondrial membranes, exposing its dehydrogenase domain to the matrix space and its putative mRNA-binding domain to the cytosol, such a topoiogy has not been seen for any mitochondrial protein. Even
the surface of the mitocho~dria for specific I@NAs, and such in oitm assays will be needed to determine whether
instead for candidate organelle-specific mR~A-binding proteins in the cytoplasm. As suggested by Preiss et al., larger eukaryotes may h,we a more complicated machinery to ensure protein targeting to the mitochondria, and we all anticipate an exciting time ahead in this field of research.
Bundoora
iochemistry, !_a Krobe University, 3083, Australia.
welcomes letters on any topic of rest. Please note, however, that previously unpublished data and criticisms of work publlshed elsewhere cannot be accepted by this journal. Letters should be sent to: The Editor, in Biochemkal Sciences evier Trends Journals 68 Hills Road, Cambridge, UK CB2 1l.A Tre
Copyright 0 1997, Elsevier Science Ltd. All rights
reserved.096&I-r)OO4/97/$17.00
ff.
6% (1!%0)
h?cd.
i&3?
~6~h~~l.
59,
569-596 osle, M., Willter. M. and . (f988) EM50 J. :,2387-2391 N. et ai. (1990) J. 5ol. Chem. 265,2677-2681 5 Seelan, R. S. and Grossman, L. I. (1991) J. Bid. Chem. 266,19?52-19757 6 Preiss, T. and Lightowlers. R. N. (1993) J. Bal. C/x%?. 268,1@659-10667 7 Preiss, T., Hall, A. and Lightowlers, R. N. (1993) J. 43i~I. Chem. 268.24523-24526 8 Preiss, T., Sang, A. E., Chrzanowska-Lightowlers, Z. R/d.A. and Lightowlers, R. N. (1995) E5S Lert. 367,
In the recent Taking Point ‘Highways for protein delivery to the mitochondria’l Lithgow et al. raised the interesting possibility that intracellular mRNA localisation may play a role in facilitating protein transport to organelles such as the mitochondrion. Furthermore, it was ted that unidentified binding factors in the mitochondrial outer membrane may function to anchor selective mRNA species at the periphery of the organelle to aid in the co-translational tra~slocat~o~ of some mitochondria! preproteins. We wish to report a candidate for sue mRNA-binding factor, the mammalian mitochondrial enzyme g!utamate dehydrogenase. In addition to the three large subunits that are encoded by the mitochondrial genome, mammalian cytochrome c ox!dase (COx> is composed of numerous nuclear-encoded polypeptides, several of which are present as tissue-specific !soforms2. These nuclear-encoded isoforms are reported to be regulate the level of mRNA express!onR-5.In an attempt to discover whether this regulation was mediated by an
Nistochem. Cyt~~~em. 34,9%3-922
ral possible mechanisms for analattion of mitoct~ondr~~l mitochondrla would be the presence of an~ll~~pecific rn~A-bindin protein attached to the mltochon outer membrane’. Preiss et al. suggest that the enzyme glutamate dehydrogenase
Lightowlers, R. N. (1995) 291-296 and Schatz, G. (1995) ~~~~ J. 14. 239_3-2297
ase selectivity in the RNAsubstrates with which it can interact in uitd3.
in ~‘0 is its location within the mitoc~!ondrial matrix: in intact cells the protein IS separated from any mR!VA substrate by the two mitochondrial membranes. While it remains a formal possibility that glutamate dehydrogenase might actually cross both mitochondrial membranes, exposing its dehydrogenase domain to the matrix space and its putative mRNA-binding domain to the cytosol, such a topoiogy has not been seen for any mitochondrial protein. Even
the surface of the mitocho~dria for specific I@NAs, and such in oitm assays will be needed to determine whether
instead for candidate organelle-specific mR~A-binding proteins in the cytoplasm. As suggested by Preiss et al., larger eukaryotes may h,we a more complicated machinery to ensure protein targeting to the mitochondria, and we all anticipate an exciting time ahead in this field of research.
Bundoora
iochemistry, !_a Krobe University, 3083, Australia.
welcomes letters on any topic of rest. Please note, however, that previously unpublished data and criticisms of work publlshed elsewhere cannot be accepted by this journal. Letters should be sent to: The Editor, in Biochemkal Sciences evier Trends Journals 68 Hills Road, Cambridge, UK CB2 1l.A Tre
Copyright 0 1997, Elsevier Science Ltd. All rights
reserved.096&I-r)OO4/97/$17.00