SEQUENCE ELEMENTS REQUIRED FOR TRANSCRIPTIONAL ACTIVITY OF THE HUMAN MYOGLOBIN PROMOTER IN INTACT MYOCARDIUM

To define sequence elements required for myoglobin gene transcription in the intact heart, we examined the expression of a reporter gene und er the control of a 380-bp upstream segment (-373 to +7) from the huma n myoglobin gene in transgenic mouse embryos and after gene transfer i nto left ventricular myocardium of adult rats. This proximal upstream region was sufficient to direct expression of luciferase selectively i n cardiac and skeletal muscle of mouse embryos and to recapitulate the pattern of expression of the endogenous mouse myoglobin gene. This sa me upstream region was transcriptionally active after injection of pla smid DNA into the left ventricular wall of adult rats. Point mutations within two evolutionarily conserved sequence elements-a cytosine-rich (CCAC-box) motif and an A+T-rich (A/T) motif-severely impaired transc ription within the intact heart. Nuclear extracts from neonatal cardio myocytes contain protein factors that bind to each of these elements i n a sequence-specific manner. We conclude that combinatorial interacti ons between the cognate DNA binding factors that recognize these motif s are necessary for transcriptional activity of the myoglobin upstream region in cardiac muscle.