This work validates the combined action of miRNA recognition elements using target protectors.
Li N, Flynt AS, Kim HR, Solnica-Krezel L, Patton JG. Dispatched Homolog 2 is targeted by miR-214 through a combination of three weak microRNA recognition sites. Nucleic Acids Res. 2008 Jun 26. [Epub ahead of print]

End of abstract:
”...we found that a combination of weak sites, which lack canonical seed pairing, can effectively target an mRNA for silencing. This finding underscores the challenge that prediction algorithms face and emphasizes the need to experimentally validate predicted MREs.”