After entering the nucleus from the cytosol, p-S97-BMAL1:p-T451,T461-CLOCK heterodimers bind two E-boxes in the promoter of the CRY1 gene (inferred from mouse homologs). KMT2A (MLL1) associates with CLOCK and is found at E-box promoter elements (inferred from mouse homologs). KMT2A is a component of MLL1 histone acetyltransferase complexes, however, the association of other components of the MLL1 complex with CLOCK has not been demonstrated. The histone acetyltransferase CREBBP interacts with BMAL1 (inferred from mouse homologs), however, the presence of CREBBP or EP300 at the CRY1 promoter was not detected (inferred from mouse homologs). CRY1 is a repressor of transcription activation by the p-S97-BMAL1:p-T451,T461-CLOCK heterodimer and its expression thereby initiates the negative phase of the circadian cycle. NPAS2 acts redundantly with CLOCK to form heterodimers with BMAL1 and regulate CRY1 expression (inferred from mouse homologs).