Identification of sequences in the long terminal repeat of avian sarcoma virus required for efficient transcription

Two different vectors, LTR-NEO-LTR and LTR-CAT-LTR, were constructed and deletions were introduced in the upstream LTR at -299 and at -140. These deletion mutants were introduced into QT6 cells under transient expression conditions, and the levels of transcription were monitored by dot blot hybridization or by CAT assays. The results indicate that the nucleotides between -208 and -201 and between -141 and -119 in the U3 region of RSV LTR are required for efficient transcription.