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Journal of Virology, January 1999, p. 368-376, Vol. 73, No. 1
Department of Microbiology, University of
Pennsylvania School of Medicine, Philadelphia, Pennsylvania
19104-6142,1 and
Division of
Experimental Medicine, Institute of Hematological Research, Academy
of Medicine, Buenos Aires, Argentina2
Received 27 March 1998/Accepted 9 October 1998
Mouse mammary tumor virus (MMTV) infects both lymphoid tissue and
lactating mammary gland during its infectious cycle, but some
endogenous MMTVs are transcribed only in lymphoid cells. We found a
lymphoid cell-specific endogenous MMTV that was converted to a
milk-borne, infectious virus through recombination with an exogenously
transmitted MMTV. The changed expression pattern correlated with the
alteration of a single base pair in the long terminal repeat of the
lymphoid cell-specific virus. Transgenic mice with the element
from either the milk-borne or lymphoid cell-specific virus upstream of
the chloramphenicol acetyltransferase reporter gene showed the same
pattern of expression as the virus from which the regulatory sequences
were derived. Electrophoretic mobility shift assays with mammary cell
extracts showed that the site from the milk-borne virus was
preferentially bound by a prolactin-inducible factor that poorly bound
the altered site from the lymphoid cell-specific virus. The complex
that formed on the milk-borne virus-specific oligonucleotide
supershifted with anti-Stat5b antibody. Mice lacking either Stat5a or
Stat5b had dramatically reduced levels of MMTV transcripts in mammary
gland but not in lymphoid tissue. Thus, a member of the STAT family of
transcription factors is involved in the tissue-specific expression of
mouse mammary tumor virus in vivo. This is the first example of the
involvement of a member of the STAT family of transcription factors in
the control of tissue-specific expression.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Mammary Gland Expression of Mouse Mammary Tumor Virus Is
Regulated by a Novel Element in the Long Terminal Repeat


*
Corresponding author. Mailing address: University of
Pennsylvania, Room 526 CRB, 415 Curie Blvd., Philadelphia, PA
19104-6142. Phone: (215) 898-9764. Fax: (215) 573-2028. E-mail:
rosss{at}mail.med.upenn.edu.
Present address: The Jackson Laboratory, Bar Harbor, ME 04609.
Present address: The Whitehead Institute, Cambridge, MA 02142.
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