MEF2D does not directly interact with core clock components. Cotransfection of Mef2d does not lead to activation of (a) Per1::Luc (average of 2 replicates across 3 experiments; 125 ng Mef2d transfected), (b) Per2::Luc (average of 2 replicates across 2 experiments; increasing doses of Mef2d from 5 to 50 ng), or (c) Bmal1::Luc (average of 2 replicates from 1 experiment; increasing doses of Mef2d from 5 to 50 ng) in reporter assays. Both Per1::Luc and Per2::Luc activation is observed in the presence of known transcriptional activators, BMAL1 and CLOCK (Per1: F(3,20) = 10.80; **p = 0.0002; Per2: F(10,33) = 3.42, p = 0.0037, not significant after correction for multiple comparisons). d, Cotransfection of Mef2d activates a Mef2 binding domain fused to a TATA box (average of 2 replicates across 2 experiments; 125 ng Mef2d transfected; t(3.127) = 8.472; *p = 0.029). e, MEF2D is not pulled down with BMAL1 in coimmunoprecipitation experiments, whereas the known binding partner, CLOCK, was successfully coimmunoprecipitated and FLAG (BMAL1) enrichment is observed.