RNA looping has been reported for other RNA-binding proteins, including the alternative splicing regulator PTB (Oberstrass et al., 2005, Auweter et al., 2007, Lamichhane et al., 2010), which is present at similar concentration as ZBP1 in cancer cells (Beck et al., 2011) and where the individual RRM3 and RRM4 domains bind RNA with moderate affinity (Kd in the low μM range; Auweter et al., 2007) and an ∼90-fold inter-domain coupling. The gene discussed is ZBP1; the disease is cancer.