Post-transcriptional gene regulation by RNA-binding proteins controls mRNA half-life and efficiency of translation. Recently, the RNA-binding proteins Roquin and Regnase-1 have been shown to play pivotal roles in T lymphocytes by preventing inflammatory and autoimmune disease. These factors share an overlapping set of target mRNAs and are both regulated by proteolytic cleavage through the paracaspase MALT1. This review discusses the mouse models of inactivation or deregulation and how these trans-acting factors recognize target mRNAs. Based on different affinities of cis-elements in target mRNAs and regulation of the trans-acting factors, we propose the following model: Increasing TCR signal strength will gradually inactivate Roquin and Regnase-1 causing differential target mRNA derepression that specifies cell fate decisions and effector functions of T cells.