Abstract
MicroRNAs are post-transcriptional regulators that control mRNA stability and the translation efficiency of their target genes. Mature microRNAs are approximately 22-nucleotide in length. They mediate post-transcriptional gene regulation by binding to the imperfect complementary sequences (a.k.a. microRNA regulatory elements, MRE) in the target mRNAs. It is estimated that more than one-third of the protein-coding genes in the human genome are regulated by microRNAs. The experimental methods to examine the interaction between the microRNA and its targeting site(s) in the mRNA are important for understanding microRNA functions. The luciferase reporter gene assay has recently been adapted to test the effect of microRNAs. In this chapter, we use a previously identified miR-138 targeting site in the 3'-untranslated region (3'-UTR) of the RhoC mRNA as an example to describe a quick method for testing the interaction of microRNA and mRNA.