Re: Re: junk DNA or buffer DNA?

Geoff Smith (
Tue, 17 Mar 1998 21:00:07 -0800

> From: CurtAdams <>
> To:
> Subject: Re: Re: junk DNA or buffer DNA?
> Date: Tuesday, March 17, 1998 7:56 PM
> In a message dated 3/17/98 1:22:52 PM, wrote:
> >> From: Hal Finney <>
> >
> >> I don't see how that would work. Just adding more junk DNA will not
> >> reduce the number of mutations in the coding DNA. The mutation rate
> >> presumably constant per base.
> >
> >
> >This may be a bad presumption. I have seen many assume that mutation
> >is constant per base, but I have never seen a validation of that
> >assumption. If mutagens are in any way significant in causing mutation,
> >mutation rate will not be constant per base, as the amount of most
> >is not directly related to the number of base pairs. (eg. UV radiation)
> >would assume that for these mutagens, number of mutations has a greater
> >relation to the amount of mutagen than the number of base pairs.
> Twice as many base pairs means twice as many UV hits at a given flux.
> just not enough DNA, even in animals, to screen an appreciable amount of

I would think lower wavelength EM radiation would be screened by the
massive clumps of DNA that exist in a eukaryotic cell, especially
non-coding sequences which(interestingly enough) tend to clump up to a very
high degree in a bundle of nucleotides and histones. Maybe the low
wavelength I'm talking about it not very common (cosmic/gamma rays, maybe?)

> The idea you have would have two main requirements:
> 1) The exposure of the cell to the mutagen cannot depend on the amount of

> DNA in the cell. Direct radiation is out, although free radicals from
> radiation would be OK.

Along with free radicals from metabolic processes, free radicals from the
environment, and other chemical mutagens.

> 2) The mutagen must be largely eliminated by mutating DNA. If the mutagen
> is largely cleared by any other process, increasing DNA will just
> the proportion "cleared" by affecting DNA. Also, if the mutagen is
> not destroyed or inactivated by mutating DNA, then obviously extra DNA
> doesn't help.
> The only mutagen I know of that would meet qualification 2 is other DNA.

Try most carcinogens. Most carcinogens work by binding to areas of DNA
during cell division. The replication process has to skip this part of the
DNA, causing a massive deletion. Obviously, if such a mutagen is bound, it
will only mutate that particularly area, and no others. Thus, it is
"cleared" in this sense.

hmmm... I think I may have something there, what do you think?

> The idea that "junk" DNA provides a distraction for all those transposons
> hopping around has been suggested, although I don't know where.

Also a good explanation. A good way to test this hypothesis would be to
look for transposon binding/recombination sequences in junk DNA.