Transcription activation by a sliding clamp

Area of Science:

• Molecular Biology
• Structural Biology
• Virology

Background:

• Bacteriophage T4 late gene transcription requires a complex of RNA polymerase (RNAP), gp55, gp33, and gp45.
• Previous studies provided genetic and biochemical insights, but lacked structural details of the transcription machinery.
• Understanding this complex is crucial for deciphering viral gene expression regulation.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopy (cryo-EM) structures of key bacteriophage T4 transcription complexes.
• To elucidate the molecular interactions governing T4 late gene promoter recognition and transcription activation.
• To provide structural basis for the roles of gp55, gp33, and gp45 in the transcription process.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to resolve complex structures.
• Structures were determined for a gp55-dependent RNAP-promoter open complex.
• An intact gp45-dependent transcription activation complex structure was also obtained.

Main Results:

• The structures reveal specific interactions between gp55 and T4 late promoter DNA.
• Gp55 utilizes a σR2 homology domain and a helix-loop-helix motif to bind single-stranded DNA within the transcription bubble.
• Gp33 interacts with both RNAP and upstream DNA, while gp45 encircles DNA, tethering RNAP and potentially facilitating 1D scanning.

Conclusions:

• The study provides unprecedented structural insights into bacteriophage T4 late gene transcription activation.
• The findings detail the mechanism of promoter recognition by gp55 and the role of gp45 in enhancing transcription efficiency.
• These structures offer a foundation for understanding viral transcription regulation at a molecular level.