Evaluation of the enhancer function of LCR sequences with homologous and heterologous promoters by transient transfection analysis in mammalian cells. Transient transfections of MeWo (A), B16 (B, E and F), D407 (C) and PC12 (D) cells, using HS, SH, X, HSΔA (ΔA), HSΔB (ΔB), HSΔAB (ΔAB) or none (–) LCR-derived fragments in combination with pTLuc (white bars), pTKLuc (grey bars) heterologous promoters and pTyrLuc (black bars) homologous promoter backbone plasmids (Fig. 1). Results are expressed as relative transactivation, arbitrarily assigning to backbone promoter-only plasmids (pTLuc, pTKLuc and pTyrLuc, respectively) the value of x1 and thereafter referring the activity of each construct to its corresponding promoter-only plasmid. In PC12 and D407 cells, tyrosinase promoter constructs produced luciferase reporter expression values close to background. Normalisation of the luciferase reporter values between different transfected constructs is achieved taking into account the activity of a co-transfected lacZ reporter plasmid and the number of pmols of experimental plasmid DNA used in each transfection. See Materials and Methods for plasmid sizes. Relative transactivations are mean values from triplicate experiments (±SD).