Persistence of separate mitochondrial genome

Mark Dowton mdowton at uow.edu.au
Mon Sep 18 18:16:22 EST 2000

Hi Daniel,

One piece of evidence contra this idea is that, in plastids, rbcL (which is 
normally encoded by plastids) can be engineered into the nuclear genome,
deleted from the plastid, yet full expression of the chloroplast
targeted rbcL occurs (Kanevski & Malaga: Relocation of the plastid rbcL gene 
to the nucleus yields functional rubisco in tobacco chloroplasts: PNAS 91:
1969).  Although I realise this is a round-about way of addressing
your point, it suggests that proteins encoded by organellar genomes can be 
relocated to the nucleus, but that there is a selective advantage in their
location within the organelle.

Cheers, Mark

Daniel B Davison wrote:

> Hi all,
> I thought I remembered discussion from ~25 years ago that the main reason 
> for the maintenance of
> mitochondrial genomes were that the proteins encoded by mtDNA were 
> extremely hydrophobic. Under this
> hypothesis, they had minimal chances of crossing the cytoplasm and multiple 
> membrances. mtDNA ensured that
> the proteins were made at the site they were needed.
> Thanks,
> dan davison
> David Mathog wrote:
> > In article <8pr430$s9c$1 at mercury.hgmp.mrc.ac.uk>, Dr. Ram Samudrala <ram.samudrala at stanford.edu> writes:
> > >
> > >I would turn that around and ask: why do you think they should go to
> > >the nucleus?  It seems a system that works well initially evolved this
> > >way---what selective advantage do you see to those genes being in the
> > >nucleus as opposed to being in the mitochondrion.
> >
> > Advantages: Recombination and diploidy (or higher).   The genes of the
> > organelle needn't be perfectly adapted at all times - think about what
> > happens when one suffers a deleterious mutation.  Sex is good for the
> > genes, but organelles don't have sex, only cells containing organelles do.
> >
> > I also suspect that the repair of DNA mutations is much better for nuclear
> > genes.  Although that probably was't true the day the first organelle
> > crawled into the cytoplasm, the first two factors would lead to nuclear
> > migration of genes, and that would tend to break the DNA repair systems in
> > the organelle.
> >
> > Regards,
> >
> > David Mathog
> > mathog at seqaxp.bio.caltech.edu
> > Manager, sequence analysis facility, biology division, Caltech
> >
> > ---
> ---

Mark Dowton
Australian Flora and Fauna Research Centre
Dept Biology
Wollongong University
Wollongong  NSW  2522
Phone: 61-2-42215897
Fax: 61-2-42214135
Email: mdowton at uow.edu.au


Dept Applied and Molecular Ecology
Waite Campus, Adelaide University
PMB #1
Glen Osmond  SA  5064

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