FIG. 1.

MPEX is required for full MCK enhancer-promoter activity in skeletal and cardiac myocytes. (A) Partial sequence alignment of MCK promoter (−85 to −51 for mouse) from multiple mammalian species. The MPEX sequence (solid line) and a conserved 3′ region (dashed line) are indicated. The wild-type mouse sequence (WT) used as a probe in Fig. 2A, as well as mutations within this sequence (M1, M2, and M3), tested in panels B and C and Fig. 2A, are shown. Unaltered bases are indicated as asterisks. (B and C) Analysis of MPEX mutations in skeletal (B) or cardiac (C) myocytes. MM14 skeletal myocytes or primary neonatal cardiomyocytes were transfected with constructs containing the CAT reporter under the control of either the 358-bp MCK promoter (−358MCKCAT) or the MCK enhancer linked to the promoter (enh-358MCKCAT) and the PAP reference plasmid. Activities of the wild-type constructs compared to those of constructs containing mutation M1, M2, or M3 are shown. For each panel, data are plotted as the mean value and standard deviation of the CAT/PAP ratio determined for each culture dish, and the activity of the wild-type construct is set at 100.