DNA exchange between mitos and (NUCLEAR) genome

John Logsdon jlogsdon at bio.indiana.edu
Thu Jul 22 11:01:23 EST 1993

In article <1993Jul22.080240.5591 at gserv1.dl.ac.uk> ,
suter at VAX.MPIZ-KOELN.mpg.d400.de writes:
> it's artifact time again.

Well not really, depending on your perspective ;-}.
> i have tagged a genomic region in tobacco with t-dna, and behold,
> after sequencing the genomic clone, i find in the middle of it a
> with 70% homology (over 140 bp) to a mitochondrial locus from
> arabidopsis. if you would look at a smaller range, the homology is even
> better.
> questions: is there an exchange of genetic material possible between 
> mitos and chromosome ? do you know of any other examples (perhaps with
> a recent paper, so that i can backsearch) ?

The general area is called "Promiscuous DNA"  (reviewed in TIBS 9:271
(1984)). There is now quite a bit of precedent for this phenomenon of 
organelle ----> nuclear DNA movement (also organelle ---->organelle)
.This phenomenon is extremely relevant to the process/mechanisms of "gene
transfer" from organelles to the nucleus (and sometimes between
organelles). Recall that most organelle proteins are nuclear-localized
and are a result of post-endosymbiotic transfer. Successful gene transfer
is (currently) a rare, but ongoing process (see Nature.344: 262 (1990)).
DNA movement, on the other hand, is probably a frequent process, most
events which do not lead to succesful gene movement.  Therefore, most of
the organelle DNA that you would find in the nucleus is probably just a
result of a failed "experiment" in gene transfer.  From these cases
recent of DNA movement, one can learn about some of the underlying
mechanisms by which DNA (or RNA) is moved between compartments.

Here are a few more recent references to start with:

Chloroplast -----> Nucleus
Mol Gen Genet 225: 453-458 (1991)  (my contribution to this area :-} )
Mol Gen Genet 236: 105-112 (1992) (Timmis' group is the leader in this)
Theor Appl Genet 85: 229-238 (1992) (more from Timmis)

Mitochondrion -----> Nucleus
J Mol Biol 210: 703-707 (1989) (human)
J Mol Biol 221: 1223-1235 (1991) (rat)
J Mol Biol 222: 525-536 (1991) (_Toxoplasma_)
Mol Biol Evol 9: 204-215 (1992) (rodent)
Nature 346: 376-379 (1990)(a NEAT *experimental* study in yeast)

Chloroplast  ---> Mitochondrion
Mol Gen Genet  236: 341-346 (1993) 

I thope that this is a start!

As far as I know (I am now only a casual observer of the field now),
there is no documented case of mtDNA in the nuDNA of plants. The
situation that you have discovered in Arabidopsis may be quite novel.

John Logsdon         Department of Biology
                     Indiana University
                     Bloomington, IN  47405
                     (812) 855-2549
                     (812) 855-6705 fax

jlogsdon at bio.indiana.edu

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