The mechanism of transcriptional activation by the topologically DNA-linked sliding clamp of bacteriophage T4.
J Mol Biol
; 321(5): 767-84, 2002 Aug 30.
Article
en En
| MEDLINE
| ID: mdl-12206760
Three viral proteins participate directly in transcription of bacteriophage T4 late genes: the sigma-family protein gp55 provides promoter recognition, gp33 is the co-activator, and gp45 is the activator of transcription; gp33 also represses transcription in the absence of gp45. Transcriptional activation by gp45, the toroidal sliding clamp of the T4 DNA polymerase holoenzyme, requires assembly at primer-template junctions by its clamp loader. The mechanism of transcriptional activation has been analyzed by examining rates of formation of open promoter complexes. The basal gp55-RNA polymerase holoenzyme is only weakly held in its initially formed closed promoter complex, which subsequently opens very slowly. Activation ( approximately 320-fold in this work) increases affinity in the closed complex and accelerates promoter opening. Promoter opening by gp55 is also thermo-irreversible: the T4 late promoter does not open at 0 degrees C, but once opened at 30 degrees C remains open upon shift to the lower temperature. At a hybrid promoter for sigma(70) and gp55-holoenzymes, only gp55 confers thermo-irreversibility of promoter opening. Interaction of gp45 with a C-terminal epitope of gp33 is essential for the co-activator function of gp33.
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Bases de datos:
MEDLINE
Asunto principal:
Regulación Viral de la Expresión Génica
/
Activación Transcripcional
/
Bacteriófago T4
Idioma:
En
Revista:
J Mol Biol
Año:
2002
Tipo del documento:
Article
País de afiliación:
Estados Unidos