Regulation and function of poised mRNAs in lymphocytes

Pre‐existing but untranslated or ‘poised’ mRNA exists as a means to rapidly induce the production of specific proteins in response to stimuli and as a safeguard to limit the actions of these proteins. The translation of poised mRNA enables immune cells to express quickly genes that enhance immune responses. The molecular mechanisms that repress the translation of poised mRNA and, upon stimulation, enable translation have yet to be elucidated. They likely reflect intrinsic properties of the mRNAs and their interactions with trans‐acting factors that direct poised mRNAs away from or into the ribosome. Here, I discuss mechanisms by which this might be regulated. Poised transcripts are messenger RNAs that are not being translated but can be translated in response to stimuli. In lymphocytes poised transcripts encode cytokines and other proteins involved in cell fate. Candidate mechanisms for reversible transcript poising involving RNA binding proteins and the chemical, structural or spatial modification of mRNA are considered here.