Re: Dinofarts / Sauropod methane emissions

[Erik Boehm <erikboehm07@yahoo.com>]

> That's extremely easy and inevitable! Any time an
> endosymbiote breaks up (for whatever reason) inside the host
> cell, its DNA can end up in the nucleus.

Yes, but that doesn't answer the mechanism by which it crosses the nuclear 
pore, or integrates with the nuclear chromosomes.
Given that the gene loss in mitochondria is not uniform in Eukaryotes, 
mitochondrial genes were clearly still being transfered to the host genome 
after the nucleus and nuclear pore had developed.

Yes, it seems obvious that if the endosymbiont lyses, that its DNA will be in 
the cytoplasm (where it normally won't be last very long).

But from there, its not clear.
The nuclear envelope disappears during mitosis - is there an increased chance 
of a mitochondrial gene becoming part of the nuclear genome then? Even though 
the nuclear DNA is compacted at that point. When the new envelop forms, is 
mtDNA sometimes engulfed?
Or did it simply cross the nuclear pore during, lets say, S phase?

Was its integration transposon mediated?
Presumably the ancestral mitochondria had many genes that were redundant with 
the nuclear genes (such as polymerases), presumably there was sequence homology 
- was the gene transfer mainly by homologous recombination of those genes? or 
did those redundant genes simply get lost in the mitochondria and the remaining 
genes were integrated by another mechanism.
Did it occur by double strand break repair?
Was it random insertion?
All of the above?

Its clear it happened, its clear that you have the mitochondrial DNA in close 
proximity to nuclear DNA with only one pore to cross, and thus the barriers to 
getting endosymbiont DNA into the nucleus are much lower than DNA external to 
the cell.
But the specifics beyond that are not clear (at least not to me)- but it does 
not seem like it would be hard.

--- On Wed, 5/9/12, David Marjanovic <david.marjanovic@gmx.at> wrote:

> From: David Marjanovic <david.marjanovic@gmx.at>
> Subject: Re: Dinofarts / Sauropod methane emissions
> To: "DML" <dinosaur@usc.edu>
> Date: Wednesday, Ma
idates and can speculate),
> >  genes from the ancestor of mitochondria have been
> moved to the
> >  nucleus.
> 
> That's extremely easy and inevitable! Any time an
> endosymbiote breaks up (for whatever reason) inside the host
> cell, its DNA can end up in the nucleus. DNA that lies
> around in a eukaryotic cell can always end up in the
> nucleus. All eukaryotes contain genes of clearly
> mitochondrial origin, and it's apparently extremely common
> to have pseudogenes of mitochondrial origin. (Where
> chloroplasts are or were present, the same holds for genes
> of chloroplast...ic origin.) The entire mitochondrial genome
> often ends up as a pseudogene in the nucleus; such numts --
> nuclear copies of the mt genome -- are common enough to have
> messed with phylogenetics (there's a case in elephants I
> dimly remember), because they were mistakenly isolated along
> with mtDNA.
> 
> This is the most parsimonious way to account for the many
> bacterial genes that all eukaryotes share.
>