The bet gene of feline foamy virus is required for virus replication

Foamy viruses (FV) are complex retroviruses with additional bel genes locat ed between env and the 3' long-terminal repeat. The functions of the bel 2 and bet genes are unknown and both are dispensable for replication of the p rototypic human foamy virus in cell cultures. We examined the function(s) o f bel 2 and bet of the distantly related feline foamy virus (FFV) in the pr oviral context. Mutagenesis was used to alter the Bel 2 and Bet or to abrog ate their expression, The Bel 2/Bet mutants showed a 1000-fold reduced vira l titer in feline kidney cells; in human 293T cells, viral titer was only a bout 10-fold reduced compared to wild-type FFV In both cell types, the Bel 2/Bet mutations resulted in a reduced release of FFV particles. The results indicate that FFV Bet is required for efficient virus replication. The fun ctions of the Bel 2 and Bet proteins are discussed. (C) 2001 Academic Press .