Proteolytic Processing and Assembly of gag and gag-pol Proteins of TED, a Baculovirus-Associated Retrotransposon of the Gypsy Family

AUTOR(ES)

Hajek, Kathryn L.

FONTE

American Society for Microbiology

RESUMO

TED (transposable element D) is an env-containing member of the gypsy family of retrotransposons that represents a possible retrovirus of invertebrates. This lepidopteran (moth) retroelement contains gag and pol genes that encode proteins capable of forming viruslike particles (VLP) with reverse transcriptase. Since VLP are likely intermediates in TED transposition, we investigated the roles of gag and pol in TED capsid assembly and maturation. By using constructed baculovirus vectors and TED Gag-specific antiserum, we show that the principal translation product of gag (Pr55gag) is cleaved to produce a single VLP structural protein, p37gag. Replacement of Asp436 within the retrovirus-like active site of the pol-encoded protease (PR) abolished Pr55gag cleavage and demonstrated the requirement for PR in capsid processing. As shown by expression of an in-frame fusion of TED gag and pol, PR is derived from the Gag-Pol polyprotein Pr195gag-pol. The PR cleavage site within Pr55gag was mapped to a position near the junction of a basic, nucleocapsid-like domain and a C-terminal acidic domain. Once released by cleavage, the C-terminal fragment was not detected. This acidic fragment was dispensable for VLP assembly, as demonstrated by the formation of VLP by C-terminal Pr55gag truncation proteins and replacement of the acidic domain with a heterologous protein. In contrast, C-terminal deletions that extended into the adjacent nucleocapsid-like domain of Pr55gag abolished VLP recovery and demonstrated that this central region contributes to VLP assembly or stability, or both. Collectively, these data suggest that the single TED protein p37gag provides both capsid and nucleocapsid functions. TED may therefore use a simple processing strategy for VLP assembly and genome packaging.

Documentos Relacionados

• Gene organization and transcription of TED, a lepidopteran retrotransposon integrated within the baculovirus genome.
• The baculovirus-integrated retrotransposon TED encodes gag and pol proteins that assemble into viruslike particles with reverse transcriptase.
• Mutational analysis of the gag-pol junction of Moloney murine leukemia virus: requirements for expression of the gag-pol fusion protein.
• Expression of the gag-pol fusion protein of Moloney murine leukemia virus without gag protein does not induce virion formation or proteolytic processing.
• Structure of glycosylated and unglycosylated gag and gag-pol precursor proteins of Moloney murine leukemia virus.