miRNA in different size - (Sep/17/2007 )

it seems that some miRNA species are in different size based on Northern hybridization, is there any special in function?

well lenght of a fragment is determined by th length between the RNA binding domains of Dicer and its RNAse III domains. So i guess the higher length of the RNA may come as an intrinsic difficulty to curve the RNA, or a prefered recognition site for either RNAseIII or RNA BD of dicer.

I've noticed that too. And some miRNAs, particularly some belonging to large miRNA families, has been cloned as mixtures of 21-22nt or 20-21nt species, so they definitely exist with different size. Maybe different pre-miRNAs, possibly expressed in different or in the same tissue, are processed by dicer (or dicer-like, in plants) in different ways. I can't remember any functional role associated to this observation, but I guess that the affinity for the target should change with the size of the miRNA.