Simian foamy virus type 1 contains a second promoter located at the 3' end of the env gene.

Simian foamy virus type 1 (SFV-1) is a member of a distinct subfamily of retroviruses that possess a complex genome organization as well as complex means of regulating gene expression. This virus encodes a transcriptional transactivator (taf) that dramatically increases gene expression directed by the viral long terminal repeat. In this report, the identification of a second promoter which is significantly transactivated by SFV-1 Taf is described. The second promoter is located at the 3' end of SFV-1 env gene downstream from position 8158 (1 represents the first nucleotide sequence of the viral genome). Deletion analysis indicated that there are at least two targets for Taf in the internal promoter. A time-course analysis of SFV-1 gene expression showed that the messages for the regulatory genes were generated prior to the transcription of the structural proteins. Therefore, SFV-1 replication may be regulated by mechanisms that involve a temporal pattern of gene expression. The potential role of the internal promoter in SFV-1 gene expression and replication is discussed.