BACKGROUND: Cart1 encodes the paired-like homeodomain in the central portion of 
the gene, and plays a crucial role in the developmental lineage of bone and 
cartilage, especially in head formation. However, its transactivation mechanism 
is still poorly understood, including the target gene. Here, we report 
biochemical dissections of Cart1 functional domains and a relationship between 
dimerization and transcription activity.
RESULTS: Deletion studies of GAL4-fused Cart1 indicated that the transactivation 
domain is located in the middle portion of the C-terminal domain, but the 
N-terminal is also required for a full activation of the consensus palindromic 
binding site (TAATNNNATTA). Analysis of the basic amino acid residues at both 
ends of the homeodomain revealed that both sides act as nuclear localization 
signals, and are necessary for the cooperative binding to the palindromic 
sequence. In this study, two additional Cart1 isoforms that behave as dominant 
negatives were identified from rat chondrosarcoma cells. These isoforms 
suppressed the transcription activity of the wild-type, despite loss of DNA 
binding ability, and could interact with the wild-type in yeast. Finally, we 
demonstrated that wild-type Cart1 forms a DNA-independent homodimer in in vivo 
conditions, and that the transactivation of wild-type Cart1 was suppressed by 
the N- or C-terminal domain which was expressed in the nucleus.
CONCLUSION: These results revealed that homodimerization through direct 
interaction is necessary for the potent transcription activity of Cart1.