Importance of ECL1 for the constitutive activation of the E92K mutant.

Constitutive CREB activity and cell surface expression (ELISA) of wt and E92K Mc1r-Mc4r chimeras and ECL1 mutants in transiently transfected HEK293 cells.CREB activity and ELISA data are normalized to the Mc1r wt level at 2.5 ng DNA/well and given in percent as mean ± SEM. The relative constitutive activity (RCA) is calculated by normalizing the CREB activity to the cell surface expression at 2.5 ng DNA/well as described in Materials and methods and is given relative to the RCA of Mc1r wt. The fold change between the RCA values of the wt and E92K constructs on a given background is presented as ΔRCA.