A dimer of the phosphorylated BMAL1:CLOCK heterodimer binds adjacent E-boxes (EE element, E1E2 element) in the promoter of the PER1 gene (inferred from mouse homologs). Phosphorylated BMAL1:CLOCK also binds three or four other sites in the PER1 promoter (inferred from mouse homologs). Phosphorylated BMAL1:CLOCK recruits the histone acetyltransferase CREBBP and the histone methyltransferase KMT2A (MLL1) (inferred from the Bmal1:Clock complex at the Per2 promoter in Katada and Sassone-Corsi 2010). CREBBP interacts with BMAL1 and KMT2A interacts with CLOCK (inferred from mouse homologs). KMT2A forms MLL1 complexes with other factors but it is unknown which of these factors are present in the complex with BMAL1:CLOCK. NPAS2 can dimerize with BMAL1 in place of CLOCK and the BMAL1:NPAS2 heterodimer binds E-boxes and regulates expression of PER1 (inferred from mouse homologs).