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. 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 (By similarity). Binds DNA as a dimer. Interacts with CDC34. Interacts with FHL5. Isoform delta forms a heterodimer with CREB3L4. May interact with TSSK4. Isoform Tau is expressed in testis germ cells. CREM-theta1- and CREM-theta2-containing isoforms are expressed in testis. Stimulated by phosphorylation. Phosphorylated on Ser-116 by TSSK4 in vitro. Ubiquitinated by CDC34 and RAD6B in order to be degraded by the proteasome. Produced by alternative splicing. Produced by alternative promoter usage. Activator. Produced by alternative promoter usage. Activator. Produced by alternative promoter usage. Activator. Belongs to the bZIP family.