Why Uracil?

[Cornelius Krasel]

Roger J. Young (RYoung at lib.drury.edu) wrote:
> With apologies if this is the incorrect newsgroup; but the question came up
> yesterday as to why RNA uses Uracil rather than Thymine.

To make evolutionary sense, you have to ask the question the other way 
round: why does DNA use Thymine instead of Uracil?

Reasons (supposedly):
- DNA uses deoxyribose since it is chemically more stable than ribose,
  essential for hereditary material.
- As far as I recall, having Thymine in DNA instead of Uracil is
  advantageous for some DNA repair mechanism. Don't ask me details -
  I knew them once, but I forgot :-(

There is no sterical reason why Thymine did replace Uracil.

--Cornelius.

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/* Cornelius Krasel, U Wuerzburg, Dept. of Pharmacology, Versbacher Str. 9 */
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