Re: Re: junk DNA or buffer DNA?

CurtAdams (
Tue, 17 Mar 1998 22:56:25 EST

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 is
>> presumably constant per base.
>This may be a bad presumption. I have seen many assume that mutation rate
>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 mutation
>is not directly related to the number of base pairs. (eg. UV radiation) I
>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. There's
just not enough DNA, even in animals, to screen an appreciable amount of UV.

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.

2) The mutagen must be largely eliminated by mutating DNA. If the mutagen
is largely cleared by any other process, increasing DNA will just increase
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.
The idea that "junk" DNA provides a distraction for all those transposons
hopping around has been suggested, although I don't know where.