Muscle-specific transcriptional activation by CArG box requires either homophilic or heterophilic interactions of the CArG box binding factors.

CArG boxes (CC(A/T)6GG sequences) are present in various promoters and are able to confer two different types of transcriptional responsiveness: serum inducibility and muscle-specific activation. Inserted upstream from the ubiquitous HSV thymidine kinase promoter, multimerized HCA1 boxes (human cardiac alpha-actin proximal CArG box) behave as strong muscle-specific activating elements. Transient expression assay was used to determine whether the muscle-specific transcriptional activation by the CArG boxes depends on the presence in the vicinity of other specific cis-acting DNA elements. Our results show that no specific association between different regulatory binding sites is required for the myogenic activity of a CArG box and that CArG elements are able to stimulate transcription in myogenic cells through either homophilic or heterophilic interactions of the CArG box binding factors.