AEGiS-14IAC: The HIV-1 Tat Protein Can Promote Both the First Strand Transfer in Reverse Transcription and Annealing of tRNALys3 onto the Primer-Binding Site (PBS).

14th International AIDS Conference

Barcelona, Spain - July 7-12, 2002

The HIV-1 Tat Protein Can Promote Both the First Strand Transfer in Reverse Transcription and Annealing of tRNALys3 onto the Primer-Binding Site (PBS).

Int Conf AIDS 2002 Jul 7-12; 14:(abstract no. WeOrA1259)

Wainberg MA, Kameoka M, Liang C, Guo X
McGill University AIDS Centre, Montreal, Canada

BACKGROUND: We previously demonstrated that wild-type Tat can augment viral infectivity by suppressing the reverse transcriptase (RT) reaction at late stages of the viral life cycle to prevent the premature synthesis of potentially deletirious viral DNA products.

METHODS: We have performed a detailed analysis of the cell-free reverse transcription reaction to elucidate the mechanisms(s) whereby Tat can affect this process.

RESULTS: Tat can suppress non-specific DNA elongation, due largely to sequences contained within the second Tat exon, while moderately affecting the specific initiation stage of reverse transcription. In addition, Tat has an RNA annealing activity, and can promote the placement of tRNA onto RNA as well as promote the first strand transfer in reverse transcription. This points to a functional homology between Tat and the viral nucleocapsid (NC) protein that is known to be directly involved in this process. Experiments using a series of mutant Tat proteins revealed that the cysteine-rich and core domains of Tat are responsible for suppression of DNA elongation, while each of the cysteine-rich, core and basis domains, as well as a glutamine-rich region in the C-terminal domain, are important for the placement of tRNA onto the viral RNA genome. The role of Tat in strand transfer was localized to the cys-rich region of Tat molecules containing only the first exon. These results suggest that Tat can play at least three different roles in the RT reaction, i.e. suppression of DNA polymerization, placement of tRNA onto viral RNA, and strand transfer.

CONCLUSION: The first of these activities of Tat is localized to the second exon and may contribute to the overall efficiency of reverse transcription of the viral genome during a new round of infection as well as to the enhanced production of infectious viral particles.

Keywords: AEGIS, Gene Products, tat, Transcription, Genetic, RNA, Viral, DNA, Viral, Binding Sites, RNA-Directed DNA Polymerase, RNA, DNA Primers, RNA, Transfer, Exons, genetics

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