Author/Editor     Okamoto, Hiroshi; Peterlin, B Matija; Cujec, Thomas P
Title     Mechanisms by which the HIV-encoded Tat protein increases the efficiency of transcriptional elongation by RNA polymerase II
Translated title     Mehanizem HIV-kodiranega Tat proteina, s katerim poveča učinkovitost transkripcije z RNA polimerazo II
Type     članek
Source     Acta Biol Slov
Vol. and No.     Letnik 43, št. 1-2
Publication year     2000
Volume     str. 99-108
Language     eng
Abstract     HIV encodes the transcriptional trans-activator Tat, which binds to thc trans-activation response (TAR) RNA stem-loop in the viral long terminal repeat (LTR) promoter and increases the rate of transcriptional elongation by RNA polymerase II (pol II). Tat increascs pol lI processivity by interacting with two serine/threonine kinases, namely CDK7 (a component of TFIIH) and CDK9 (which together with cyclin T1 forms the positive transcription elongation factor P-TEFb). Tat binds to CDK7 and increases its ability to phosphorylate the C-terminal domain (CTD) of pol lI. Inhibition of CDK7 kinase activity with a pseudosubstrate peptide abolishes Tat activation in vitro, as well as Tat activation and HIV replication in vivo. In addition, Tat also binds to the P-TEFb complex via cyclin T1; this interaction facilitates the binding of Tat to TAR and is absolutely required for Tat function. Significantly, the introduction of human cyclin T1 into rodent cells confers onto Tat its ability to bind TAR efficiently and to activate transcription from the HIV-LTR. The region of cyclin T1 required for efficient binding of Tat to TAR has been mapped. We conclude that P-TEFb functions to modify the transcription complex at TAR, while Tat-CDK7 complexes function at an earlier step, perhaps during promoter clearance.
Summary     Virus HIV kodira transkripcijski trans-aktivator Tat, ki se veže na transaktivacijsko promotorsko mesto peclja in zanke dolge končne ponovitve virusne RNA (TAR). Tat protein poveča učinkovitost RNA polimeraze II (pol II) s povezovanjem z dvema serin/treoninskima kinazama: CDK7 (sestavni del TFIIH) in CDK9, ki skupaj s ciklinom T1 lvori pozitivni transkripcijski dejavnik Y-TEFb. Tat se veže na CDK7 in tako poveča zmogljivost fosforilacije C- terminalne domene (CTD) pol II. Inhibicija aktivnosti kinaze CDK7 s psevdosubstratnimi peptidi prepreči aktivacijo s Tat proteinom in vitro pa tudi njegovo aktivacijo in replikacijo HIV virusa in in vivo. Poleg tega se Tat preko ciklina T1 veže tudi na P-TEFb kompleks. Ta povezava olajša nadaljno vezavo Tat proteina na TAR in je neophodno potrebna za delovanje Tat proteina. Vnos ciklina T1 v celice glodalcev se kaže tudi v tem, da omogoči učinkovito vezavo Tat proteina na TAR, kar sproži transkripcijo iz dolgih končnih ponovitev HIV virusne RNA. Na ciklinu T1 smo določili regijo, ki je potrebna za učinkovito vezavo Tat proteina na TAR. Zaključimo lahko, da P-TEFb deluje tako, da spremeni transkripcijski kompleks na mestu TAR, medtem ko kompleks Tat-CDK7 deluje na zgodnejši stopnji ob začetku transkripcije.
Descriptors     GENE PRODUCTS, TAT
RNA POLYMERASE II
TRANSCRIPTION, GENETIC
HIV-1
HIV LONG TERMINAL REPEAT