INCREASE IN THE BASAL TRANSCRIPTIONAL ACTIVITY OF THE HUMAN FOAMY VIRUS INTERNAL PROMOTER BY THE HOMOLOGOUS LONG TERMINAL REPEAT PROMOTER IN CIS

The human foamy or spumaretrovirus HFV is a complex and exogenous retr ovirus that encodes several bel genes besides the three classical retr oviral genes gag, pol, and env. HFV was recently reported to contain t wo functionally active promoters that are both strongly trans-activate d by the HFV trans-activator protein Bel 1. The occurrence of a second internal cap site underscores the complexity of the HFV genome. We ha ve analysed whether there is interference between the HFV long termina l repeat promoter and the internal promoter located in the 3' end of e nv upstream of the bel genes. Recombinant clones were constructed that carry two different indicator genes, one under the control of the U3 promoter, the other under the control of the internal promoter. The po rtion of the basal transcriptional activity of the internal promoter t hat is not trans-activated by Bel 1 was increased two- to threefold in the presence of the long terminal repeat promoter. The rate of trans- activation by Bel 1 of both HFV promoters was not altered in these con structs.