BEL-1 transactivator responsive sequences in the long terminal repeat of human foamy virus

Cis-regulatory elements in the long terminal repeat (LTR) of human foamy virus (HFV) were identified by using L TR mutants to transiently express the chforamphenicol acetyf-transferase gene after co-transfection with an expression plasmid for the virus bel-1 (transactivator) gene. The R~U5 region and an element in the 5' U3 region were found to negatively influence HFV geneexpress Ion. The complete BEL-1 responsive regionwas mapped to axtend from nucleo­ tide position -471 to position -93 relative to the start of transcription. Within this region, three e,ements were ldentified that in the homologaus or a heterologous (SV40) promoter context can, independently and irrespective of their orientation, act as targets for BEL-1. Theseelementsare located between nucleotide positions -4131-378, -3611-291, and -124/-93. The target elements do not share obvious sequence homologies. The mechanism of HFV transactivation appears to be novel among the complex retroviruses and is likely to involve, as yet, undiscovered cellular DNA binding factors. Iei f993 Acadernic Press, lnc.