Crem is a transcriptional regulator that binds the cAMP response element (CRE), a sequence present in many viral and cellular promoters. Isoforms are either transcriptional activators or repressors. Isoform Delta is an activator. Crem plays a role in spermatogenesis and is involved in spermatid maturation. Binding of isoform Tau (activator) to CRE is increased by CREB3L4. The CREM isoform Tau-CREB3L4 heterodimer functions through CRE and may recruit HIRA to CRE to regulate histone exchange.