Elements in the long terminal repeat of murine retroviruses enhance stable transformation by thymidine Idnase gene

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Abstract
We have investigated the effects of long, terminal repeats (LTRs) ot murine retroviruses on the frequency of obtaining stable transfectants by the herpes virus thytaiaine kinase (TK) gene. The results indicate that addition of LTRs enhances the number of TK+ transformants by 10-20 fold. A 5-12 fold enhancement was also observed when chromosomal DNA from either numan or hamster cells was Bixed with a plasmid containing LTR– sequences anc transfected onto LTK’ cells. The LTR sequences involved in the enhancement were localizes in the region which contins tandem repeats. All other regions of the LTR did not show any enhancement of stable TK+ transfectants. The location or the orientation of the enhancer sequences with respect to the TK gene did not exert any influence on the frequency of transformation. The enhancement effect does not appear to be linked to either increased numbers of chromosomal integrations or elevated levels of transcription of the TK gene.