A Deletion Mutant of Mouse Mammary Tumour Virus, Lacking 516 Nucleotides of the 5' Long Terminal Repeat Sequence, Can Be Expressed in a Hormone-responsive Fashion

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Abstract
Summary In vitro manipulation of proviral DNA of mouse mammary tumour virus (MMTV) was used to construct mutants with defined deletions at the 5′ end of the proviral gene. In the mutants 516, 1400 and 2000 nucleotides were removed from the 5′ end. The deleted proviral DNA was tested for transcription and glucorticoid hormone regulation of viral RNA expression upon cotransfection into rat XC tk- cells with a thymidine kinase gene. Intact proviral DNA contained in the plasmid vector pBR322 and the deletion mutant pGR16Δ516, missing 516 nucleotides of the 5′ long terminal repeat (LTR) sequence, were transcribed in a hormone responsive fashion and produced RNA species of 35S and 24S. Deletion of the entire LTR sequence abolished MMTV transcription and the hormonal effect.