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J. Virol., 09 1997, 6323-6331, Vol 71, No. 9
C Baum, K Itoh, J Meyer, C Laker, Y Ito and W Ostertag
The polycythemic strain of the spleen focus-forming virus (SFFVp) contains
the most potent murine retroviral enhancer configuration known so far for
gene expression in myeloerythroid hematopoietic cells. In the present
study, we mapped two crucial elements responsible for the high activity of
the SFFVp enhancer to an altered upstream control region (UCR) containing a
GC-rich motif (5'-GGGCGGG-3') and to a unique enhancer core
(5'-TGCGGTC-3'). Acquisition of these motifs accounts for half of the
activity of the complete retroviral enhancer in hematopoietic cells,
irrespective of the developmental stage or lineage. Furthermore, the UCR
motif contains the major determinant for the enhancer activity of SFFVp in
embryonic stem (ES) cells. Using electrophoretic mobility shift assays, we
show that the UCR of SFFVp, but not of Friend murine leukemia virus, is
targeted by the ubiquitous transcriptional activator, Sp1. The core motif
of SFFVp creates a specific and high-affinity target for polyomavirus
enhancer binding protein/core binding factor (PEBP/CBF) and excludes access
of CAAT/enhancer binding protein. Cotransfection experiments with ES cells
imply that PEBP/CBF cooperates with the neighboring element, LVb (the only
conserved Ets consensus in the SFFVp enhancer), and that the Sp1 motif in
the UCR stimulates transactivation through the Ets-PEBP interaction.
Putative secondary structures of the retroviral enhancers are proposed
based on these data.
Copyright © 1997, American Society for Microbiology
The potent enhancer activity of the polycythemic strain of spleen focus- forming virus in hematopoietic cells is governed by a binding site for Sp1 in the upstream control region and by a unique enhancer core motif, creating an exclusive target for PEBP/CBF
Heinrich-Pette-Institute for Experimental Virology and Immunology, Department of Cell & Virus Genetics, Hamburg, Germany.
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