Delineation of positive and negative control elements within the promoter region of the murine leukemia inhibitory factor (LIF) gene.

Leukaemia inhibitory factor (LIF) is a multifunctional growth and differentiation factor with activities in both the adult and the embryo. The expression of LIF appears to be tightly regulated, as the levels of constitutive expression in most tissues and cell lines is extremely low. In this report we have identified three sequence elements within the 5'-flanking region of the murine LIF gene which control the constitutive action of the LIF promoter. A nested set of DNA fragments from the LIF gene 5'-flanking region was placed upstream of the chloramphenicol acetyltransferase (CAT) gene and assayed for their ability to direct chloramphenicol acetyltransferase (CAT) expression in STO-fibroblasts. The essential promoter of the LIF-gene, giving rise to low levels of CAT expression, was found to require the major start-site of transcription (+1), a TATA-box (-31) and up to 72 additional 5' nucleotides (-32 to -103). A negative regulatory element which abolished CAT-activity was identified between positions -360 and -249. The SV40 enhancer element was able to override this apparent negative element. In addition, an apparent positive control element in the LIF 5'-flanking region, between positions -860 and -661 was identified which was also able to override this negative effect.