The cardiac ankyrin repeat kinase (CARK) gene, also named TNNI3K for its 
interaction with cardiac troponin I, is both a unique expression and 
heart-enriched gene. To understand the mechanisms of CARK gene expression and 
regulation, we first cloned the full-length mRNA sequence and mapped the 
transcription start site of the mouse CARK gene and characterized its promoter 
regions. Two transcriptional isoforms of the CARK gene were identified in mouse 
heart tissue. Truncation analysis of the CARK promoter identified a minimal 151 
bp region that has strong basal transcription activity. Mutational analysis 
revealed five conserved cis-acting elements in this 151-bp long minimal 
promoter. Mutational and loss-of-functional analysis and co-transfection studies 
indicated that MEF2 binding region is the most critical cis-acting element in 
the CARK promoter, and CARK transcription level can be down-regulated by MEF2C 
antisense. Binding to the MEF2 sites by Mef2c protein was confirmed by 
electrophoretic mobility shift assay and competition and supershift 
electrophoretic mobility shift assays.