A Ubiquitous Repressor Interacting with an F9 Cell-specific Silencer and Its Functional Suppression by Differentiated Cell-specific Positive Factors

A mutant of polyomavirus, F9-5000, capable of growing in F9 cell [M. Vasseur et al., J. Virol., 43: 800-808, 1982 (1)], has a deletion in the enhancer from nucleotide 5119 to nucleotide 5142. The oligonucleotide corresponding to the deleted region (delta F9-5000 element) showed silencer activity on gene expression in F9 cells. Mobility shift assay revealed a nuclear factor, PEBP4, in F9 nuclear extract which bound to the delta F9-5000 element. Mutations introduced into the PEBP4 binding site specifically abolished its binding as well as the inhibitory effect on gene expression. After F9 cells were induced to differentiate, two more factors, PEBP2 and PEBP1, a member of AP1 family, became detectable in addition to PEBP4, and at the same time the delta F9-5000 element lost silencer activity and acquired an enhancer activity. The recognition sequence of PEBP2 as well as that of PEBP1 overlapped with that of a repressor, PEBP4. PEBP4 and PEBP3, a factor related to PEBP2, were shown to compete for binding to delta F9-5000. Interplay of a ubiquitous negative factor and differentiation-induced positive factors may represent one aspect of the gene regulation during embryonic development.