4-thioUTP reactivity

[Brennan S Sawyer]

Fellow bionetters,

Our lab has been working with 4-thioUTP for some time, and we have been 
continually debating about the reactivity of this molecule.  Will 
4-thioUTP cross-link in visible light?  If it is left in a clear eppie 
tube on the bench top will it form cross-links?  If so, how much light 
exposure is too much?  Will brown eppie tubes cut down or prevent such 
cross-linking?  I should mention we are using T7 RNA pol to transcribe 
small RNAs that contain 4-thioUs at various positions.
We regularly work with tRNA-Phe from E.coli which has a 4thioU at 
position 8, and we never worry about this tRNA forming cross-links.

Also, could some one give a brief explanation of the mechanism of 
cross-linking, we are not cross-linkers by trade.

Thank you 


Brennan Sawyer