How didd D could DNA repair have evolved?

Ari-Matti Sarn saren at Operoni.Helsinki.FI
Thu Sep 16 08:58:55 EST 1993

In article <277u9i$a3s at apakabar.cc.columbia.edu> jhj4 at namaste.cc.columbia.edu (Jeffrey Hall Jennings) writes:

>1st, as the subject alludes,   I don't know what the command is to delete a character in EMAC (the default editor that appears when one uses rn.

>Anyway, my question is regarding DNA repair enymes that prevent uncontrolled growth of a cell by changing the bases to the original base.  How could these
>enzymes have evolved?  Wouldn't the cell that has mutated to have uncontroled 
>growth be selected for?  I can't think of a scenrio where these repair enzymes
>could be selected for.

>systems that

It is true that most  DNA polymerases (those being the enzymes that, among 
other, things repair DNA) are highly conserved, i.e. they have evolved very 

It is also true that speed of growth is a strong selective advantage on
single-celled organisms.
One should, however, note that single-celled organisms don't have such 
thing as "uncontrolled growth". They grow as fast as they can, and speed of 
growth is, as stated, selected for. As replication of the genome takes a 
major part of the resources needed for cell replication, the size of the 
genome is also a selective treat.

With genomes optimised for small size, most metabolic pathways in microbes 
don't have "fall-back systems". Therefore it is of utmost importance that 
there is no errors in DNA replication. 

Enzymes for detecting and correcting replication errors are thus strongly 
selected for. "Uncontrolled growth" became an issue only when multi-celled 
organisms evolved, but by that time there already was a mechanism for DNA 
rapair. This mechanism is preserved, as it is naturally a selective 
advantage for multi-celled organisms, too.  

Hope this answered the question.

Ari-Matti Saren
saren at operoni.helsinki.fi 

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