M. Lochelt et al., THE HUMAN FOAMY VIRUS INTERNAL PROMOTER IS REQUIRED FOR EFFICIENT GENE-EXPRESSION AND INFECTIVITY, Virology, 206(1), 1995, pp. 601-610
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.