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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1996 Apr 30;93(9):4137–4141. doi: 10.1073/pnas.93.9.4137

Foamy virus reverse transcriptase is expressed independently from the Gag protein.

J Enssle 1, I Jordan 1, B Mauer 1, A Rethwilm 1
PMCID: PMC39500  PMID: 8633029

Abstract

In the foamy virus (FV) subgroup of retroviruses the pol genes are located in the +1 reading frame relative to the gag genes and possess potential ATG initiation codons in their 5' regions. This genome organization suggests either a + 1 ribosomal frameshift to generate a Gag-Pol fusion protein, similar to all other retroviruses studied so far, or new initiation of Pol translation, as used by pararetroviruses, to express the Pol protein. By using a genetic approach we have ruled out the former possibility and provide evidence for the latter. Two down-mutations (M53 and M54) of the pol ATG codon were found to abolish replication and Pol protein expression of the human FV isolate. The introduction of a new ATG in mutation M55, 3' to the down-mutated ATG of mutation M53, restored replication competence, indicating that the pol ATG functions as a translational initiation codon. Two nonsense mutants (M56 and M57), which functionally separated gag and pol with respect to potential frame-shifting sites, were also replication-competent, providing further genetic evidence that FVs express the Pol protein independently from Gag. Our results show that during a particular step of the replication cycle, FVs differ fundamentally from all other retroviruses.

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Selected References

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