Deadenylate or activate? When cells are quiescent, they undergo reversible cell cycle arrest and evince low basal metabolism. Naïve T cells are normally quiescent until they recognize cognate antigens through T cell receptor–costimulatory molecule signaling. T cell quiescence appears to be an active process, but the mechanistic details are poorly understood. Hwang et al. report that the transcription factors BTG1 and BTG2 are selectively expressed in quiescent T cells. In mice, T cells conditionally knocked out for both factors showed enhanced proliferation and a lowered threshold of activation both in vitro and in response to Listeria monocytogenes infection. Deficiency of BTG1 and BTG2 resulted in increases in global messenger RNA half-life, suggesting that messenger RNA deadenylation and degradation are important processes for maintaining T cell quiescence. Science , this issue p. 1255