Terminators: the unsung heroes of gene expression.

To be properly expressed, genes need to be accompanied by a terminator, a region downstream of the coding sequence which contains the information necessary for the maturation of the messenger RNA (mRNA) 3' end. The main event in this process is the addition of a poly(A) tail at the 3' end of the new transcript, a critical step in mRNA biology which has important consequences for the expression of genes. Here, we review the mechanism leading to cleavage and polyadenylation of newly-transcribed mRNAs and how this process can affect the final levels of gene expression. We give special attention to an aspect often overlooked, which is the effect that different terminators can have on the expression of genes. We also discuss some exciting findings connecting the choice of terminator to the biogenesis of small RNAs, which are a central part of one of the most important mechanisms of regulation of gene expression in plants.