Characterization of trans-acting factor(s) regulating beta-globin gene expression by in vivo competition.

A beta-globin/TK fusion gene was microinjected into non-erythroid cells (Ltk- cells) and erythroid cells (murine erythroleukemia (MEL) cells), and the interactions of the regulatory cellular factors with the beta-globin sequences were investigated by the in vivo competition experiment. The fusion gene was expressed efficiently in Ltk- cells. This expression was inhibited by a co-injection with a three-fold molar excess of the 5'-flanking sequence of the beta-globin gene or with a nine-fold molar excess of the mammary tumor virus LTR, but not with the alpha-globin gene. The fusion gene was expressed very poorly in the uninduced MEL cells and highly in the induced MEL cells. The co-injection of the beta-globin gene did not affect expression in the MEL cells in either uninduced or induced conditions.