Posted 15 October 2009 - 06:31 AM
Answer that question and you probably have a Nature paper in your hand! There are a couple of points I'd make. Firstly, the fact that the miRNA* is hybridizing doesn't necessarily mean that the molecule is functional/loaded into RISC - it could have been protected from degradation by e.g. sequestration in P bodies and as such not functional. And this could be a global process - i.e. all small RNAs, including the star strand, are transported to P bodies upon a certain stimulus. Yet my guess would be that the helicase, or a co-factor of the helicase, that is responsible for the unwinding of the miRNA duplex selectively protects the star strand from degradation.
But I'd love to hear the thoughts and ideas of others on this board, as I think this is a really important question!