In article <1994Jan4.035244.28464 at cs.yale.edu> johnk at loglady.ninds.nih.gov (John Kuszewski) writes:
>Are there any known cases of transmembrane structures
>made from RNA? It'd be an interesting molecular fossil
>from the RNA world.
I'd be interested in such a beastie too. There aren't any that I know
of. The charged RNA phosphate backbone would be a problem, obviously.
Any such RNA would have to have a great structure, perhaps turning
itself inside-out to present the more hydrophobic bases on its
exterior surface.
One could try to evolve something close using in vitro selection, a la
Gold, Szostak, and Joyce. Start with a randomized RNA pool and select
for molecules that partition into the nonaqueous phase of a
water-hydrophobic solvent mixture. (A student in the Gold lab tried
this experiment. I don't think anything came out of it.)
But why would you immediately assume it to be a "fossil" of the RNA
world? Why (he says, leaping nimbly onto the nearest soapbox) is RNA
considered a perfectly good molecule for basing an entire primordial
lifeform on, yet any modern RNAs are immediately assumed to be rusting
relics of the past? If one accepts that nature can build a life form
out of RNA, why is it hard to accept that evolution is quite probably
still giving RNA a try?
--
- Sean Eddy
- Laboratory of Molecular Biology, MRC, Cambridge UK
- sre at mrc-lmb.cam.ac.uk
