MicroRNAs (miRNAs) are small noncoding RNA molecules of 20-24 nucleotides that 
regulate gene expression. In animals, miRNAs form imperfect interactions with 
sequences in the 3' Untranslated region (3'UTR) of mRNAs, causing translational 
inhibition and mRNA decay. In contrast, plant miRNAs mostly associate with 
protein coding regions. Here we show that human miR-148 represses DNA 
methyltransferase 3b (Dnmt3b) gene expression through a region in its coding 
sequence. This region is evolutionary conserved and present in the Dnmt3b splice 
variants Dnmt3b1, Dnmt3b2, and Dnmt3b4, but not in the abundantly expressed 
Dnmt3b3. Whereas overexpression of miR-148 results in decreased DNMT3b1 
expression, short-hairpin RNA-mediated miR-148 repression leads to an increase 
in DNMT3b1 expression. Interestingly, mutating the putative miR-148 target site 
in Dnmt3b1 abolishes regulation by miR-148. Moreover, endogenous Dnmt3b3 mRNA, 
which lacks the putative miR-148 target site, is resistant to miR-148-mediated 
regulation. Thus, our results demonstrate that the coding sequence of Dnmt3b 
mediates regulation by the miR-148 family. More generally, we provide evidence 
that coding regions of human genes can be targeted by miRNAs, and that such a 
mechanism might play a role in determining the relative abundance of different 
splice variants.