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Journal of Virology, October 1999, p. 8669-8676, Vol. 73, No. 10
Laboratory of Genetics and Physiology,
National Institute of Diabetes, and Digestive and Kidney Diseases,
National Institutes of Health, Bethesda, Maryland 20892
Received 16 June 1999/Accepted 18 June 1999
The enhancer within the long terminal repeats (LTRs) of acquired
somatic mouse mammary tumor viruses (MMTV) can activate juxtaposed genes and induce mammary tumors. In contrast, germ line proviral MMTV
genomes are integrated in the host genome and considered to be
genetically confined transcription units. Here we demonstrate that
transcription initiated in an MMTV provirus proceeds into flanking host
sequences. We discovered multiple polyadenylated transcripts which are
induced in Stat5a null mice. These range from 1.5 kb to more than 8 kb
and are specifically expressed in mammary tissue from pregnant and
lactating mice from the 129 but not C57BL/6 strain. The RNAs emanate
from both LTRs of the endogenous MTV-3 provirus on chromosome 11 and
proceed at least 10 kb into the juxtaposed genomic territory.
Transcripts originating in the 5' LTR splice from the native splice
site within the MMTV envelope gene into at least six exons, three of
which contain functional internal splice sites. The combination of
alternative splicing and the use of several polyadenylation sites
ensure the generation of multiple transcripts. To date no significant
open reading frame has been discovered. Furthermore, we demonstrate
that transcription from the MMTV 5' LTR is highly active in the absence
of Stat5a, a transcription factor that had been shown previously to be
required for transcription from the MMTV LTR.
0022-538X/99/$04.00+0
Transcription Originating in the Long Terminal Repeats of the
Endogenous Mouse Mammary Tumor Virus MTV-3 Is Activated in
Stat5a-Null Mice and Picks Up Hitchhiking Exons
*
Corresponding author. Mailing address: Laboratory of
Genetics and Physiology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bldg. 8, Rm. 101, Bethesda, MD 20892. Phone: (301) 496-2716. Fax: (301) 480-7312. E-mail: mammary{at}nih.gov.
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