"TomHendricks474"  wrote in message
news:ceqv4t$2r6b$1{at}darwin.ediacara.org...
> Could there be a connection between UV dimer repair and
> photosynthesis? Could one lead to the other or something
> that came before lead to both?
>
> "A widely distributed enzyme, called photoreactivating
> enzyme, or DNA photolyase, repairs cyclobutane pyrimidine dimers
> in the presence of visible light. A wavelength of 370 nm is most
> effective. The enzyme binds to DNA in a light independent process,
> specifically at the site of pyrimidine dimers. In the presence of
> visible wavelength ight, the bonds linking the pyrimidine
> rings are broken, after which the enzyme can dissociate
>  in the dark...
> Mechanistic studies suggest a process akin to photosynthesis,
> with the second chromophore functioning as a light harvesting
> factor, and FADH2 functioning like the photochemical reaction
> center translating light energy to facilitate the transfer
> of an electron to the dimer and breaking the pyrimidine
> pyrimidine bonds by a free radical mechanism..."
> Biochem - Mathews , van Holde.
>
> IF and that's a big if, these two are related, then
> either dimer repair led to photosynthesis or
> photosynthesis led to dimer repair or
> something before both led to both.

Interesting.  Though it sounds to me as if modern photosynthesis
and UV repair are merely analogous, not homologous.  The LHC
of photosynthesis and the "second chromophore" of dimer repair
seem, from your description, to have little in common beyond the
fact that both capture photons, and then pass the energy on to
somewhere else.  It is a similarity in function, not in machinery.

However, it is interesting that flavins, such as FADH2, are
themselves capable of absorbing photons, even if in modern
metabolism they are mostly wrapped in enzymes so that they
don't receive many photons directly and have to get their light
energy indirectly.  It is also worth noting that flavins
are modified purines.  Your recent post about RNA as a
UV absorber does tend to suggest the idea that the first
LHCs could have been RNAs, with the energy passed from
nucleotide to nucleotide until it reached a catalytic center
at a loop or stem.
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