Identification of transcriptional elements within the long terminal repeat of Rous sarcoma virus.

Transcriptional regulatory elements within the Rous sarcoma virus long terminal repeat were examined by the construction of a series of deletions and small insertions within the U3 region of the long terminal repeat. The analysis of these mutations in chicken embryo cells and COS cells permitted the identification of important transcriptional regulatory elements. Sequences within the region 31 to 18 base pairs upstream of the RNA cap site (-31 to -18), encompassing a TATA box-like sequence, function in the selection of the correct site of transcription initiation and, in addition, augment the efficiency of transcription. These sequences are essential for virus replication. Sequences within the region -79 to -59, overlapping a CAAT box-like sequence, are not required for virus replication and have no obvious effect on viral RNA transcription in the presence of an intact TATA box. However, in mutants lacking a functional TATA sequence, mutations in this region serve to decrease the efficiency of correct transcriptional initiation events.