Abstract
Transient expression of the chloramphenicol acetyltransferase gene (cat) under the control of Simian virus 40 early enhancer/promoter complex (pAOcat) was stimulated initially by differentiation of F9 cells into primitive endoderm, but it was repressed by further differentiation into visceral endoderm. Deletion of the 72-base pairs of enhancer reduced cat expression, but the dependence on differentiation was still observed. Gel retardation Assays using enhancer or promoter sequenices revealed nuclear factors expressed in undifferentiated (stem) and visceral endoderm F9 cells. Cotransfection of pAOcat with an excess of promoter or enhancer sequence stimulated cat expression. Thus, repressor-like factors were suggested to be responsible for the differentiation-dependent control.
