THE HUMAN FOAMY VIRUS INTERNAL PROMOTER IS REQUIRED FOR EFFICIENT GENE-EXPRESSION AND INFECTIVITY

The human foamy or spumaretrovirus (HFV) is a complex retrovirus that codes for the three retroviral genes gag, pol, and env and the regulat ory and accessory bel genes. A particular feature of HFV gene expressi on was recently described: not only does the HFV provirus contain the classical retroviral long terminal repeat promoter, a second functiona lly active promoter is present in the env gene upstream of the bel gen es (M. Lochelt, W. Muranyi, and R. M. Flugel, 1993, Proc. Natl. Acad. Sci. USA 90, 7317-7321). Both, the HFV long terminal repeat promoter I and internal promoter II depend upon the HFV transcriptional transact ivator Eel 1 for efficient gene expression. The internal promoter dire cts the synthesis of functionally active Eel 1 transactivator and Bet proteins that are expressed early after HN infection. In this report, it is shown that mutation of the promoter II TATA box resulted in HFV proviral clones with a reduction in infectivity by a factor of approxi mately 100. Gene expression by promoter II TATA box mutant HFV proviru ses was reduced. HFV proviruses with the mutated promoter II TATA box used cryptic start sites of transcription upstream of the original pro moter II TATA box, resulting in an inefficient and less accurate trans criptional initiation. The reduced HN structural gene expression by th e mutated HFV proviruses was relieved by providing Eel 1 protein in tr ans. This demonstrates that HN promoter Ii-directed Eel 1 expression i s important for producing the high levels of Eel 1 that increases viru s replication. (C) 1995 Academic Press, Inc.