The transcriptional control region of the Rouse sarcoma virus long terminal repeats (LTR) was shown to contain enhancer and promoter elements located within 200 base pairs upstream from the transcription initiation site [Cullen et al. (1985) Mol. Cell. Biol. 5, 438–447]. Deletion of these elements results in significant loss of LTR transcriptional activity. In the present paper it is shown that a short alternating purine-pyrimidine sequence can restore the constitutive activity of the Rouse sarcoma virus LTR in the absence of upstream elements when inserted in close proximity to the transcription initiator site. The possible molecular bases of this phenomena are discussed.
