Identification of the promoter region of chicken anemia virus (CAV) containing a novel enhancer-like element.

The single promoter region in the cloned genome [Noteborn et al., J. Virol. 65 (1991) 3131-3139] of chicken anemia virus (CAV) in chicken T-cells was analysed via CAT assays. A unique region containing four or five near-perfect direct repeats (DR) of 21 bp with one 12-bp insert was proven to be the main transcription-activation element, with enhancer-like characteristics. PCR studies revealed that CAV isolates from across the world all contained this promoter sequence. Electrophoretic mobility-shift assays (EMSA) showed that individual DR units, as well as the 12-bp insert, can bind to nuclear factors of chicken T-cells. Competition assays revealed that the DR units bound to factors other than the 12-bp insert. A synthetic oligodeoxyribonucleotide containing an SP1-box (5'-GGGCGG) could compete with factors binding to the 12-bp insert. Purified human SP1 was shown to have very strong affinity for the 12-bp insert.