CIS-ACTING ELEMENTS THAT MEDIATE THE NEGATIVE REGULATION OF MOLONEY MURINE LEUKEMIA-VIRUS IN MOUSE EARLY EMBRYOS

We have addressed the question of the nature of Moloney murine leukemi a virus (MoMuLV) repression in mouse embryos by assaying for the trans ient expression of MoMuLV-derived constructs microinjected into early cleavage embryos. We show that the same cis-acting DNA sequences respo nsible for the block in MoMuLV expression in embryonal carcinoma cell lines operate in early embryos: (i) the MoMuLV long terminal repeat is nonfunctional, and (ii) the + 147 to + 163 repressor binding site, or negative regulatory element, negatively regulates the expression from an active promoter.