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Transfer of Tat and release of TAR RNA during the activation of the human immunodeficiency virus type‐1 transcription elongation complex
Author(s) -
Keen Nicholas J.,
Churcher Mark J.,
Karn Jonathan
Publication year - 1997
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/16.17.5260
Subject(s) - biology , transcription (linguistics) , rna , elongation , virology , microbiology and biotechnology , genetics , gene , philosophy , linguistics , materials science , ultimate tensile strength , metallurgy
The HIV‐1 trans ‐activator protein, Tat, is a potent activator of transcriptional elongation. Tat is recruited to the elongating RNA polymerase during its transit through the trans ‐activation response region (TAR) because of its ability to bind directly to TAR RNA expressed on the nascent RNA chain. We have shown that transcription complexes that have acquired Tat produce 3‐fold more full‐length transcripts than complexes not exposed to Tat. Western blotting experiments demonstrated that Tat is tightly associated with the paused polymerases. To determine whether TAR RNA also becomes attached to the transcription complex, DNA oligonucleotides were annealed to the nascent chains on the arrested complexes and the RNA was cleaved by RNase H. After cleavage, the 5′ end of the nascent chain, carrying TAR RNA, is quantitatively removed, but the 3′ end of the transcript remains associated with the transcription complex. Even after the removal of TAR RNA, transcription complexes that have been activated by Tat show enhanced processivity. We conclude that Tat, together with cellular co‐factors, becomes attached to the transcription complex and stimulates processivity, whereas TAR RNA does not play a direct role in the activation of elongation and is used simply to recruit Tat and cellular co‐factors.