Crystal structure of bacteriophage lambda cII and its DNA complex

Area of Science:

• Molecular Biology
• Structural Biology
• Virology

Background:

• The bacteriophage lambda cII protein is essential for initiating lysogeny.
• cII protein activates transcription at specific phage promoters by binding to DNA operator sites.
• Understanding the mechanism of cII-mediated transcriptional activation is crucial for phage-host interactions.

Purpose of the Study:

• To elucidate the structural basis of cII protein's interaction with its DNA operator.
• To model the cII-mediated transcriptional activation complex with RNA polymerase.
• To identify the role of the RNA polymerase alpha subunit C-terminal domain (alphaCTD) in this process.

Main Methods:

• X-ray crystallography was used to determine the structures of cII protein alone and in complex with DNA.
• Structural data was used to build a model of the activation complex involving cII, DNA, and RNA polymerase.
• Previous genetic studies were leveraged to support the proposed protein-protein interactions.

Main Results:

• The crystal structure of cII protein and its DNA operator from the P(RE) promoter were determined at high resolution.
• The structures reveal how cII binds to DNA operator sequences flanking the -35 element of phage promoters.
• A model suggests the RNA polymerase alpha subunit C-terminal domain (alphaCTD) acts as a crucial bridge between cII and the sigma subunit of RNA polymerase.

Conclusions:

• The determined structures provide atomic-level insights into cII-DNA interactions.
• The study highlights the critical role of alphaCTD in mediating cII-dependent transcriptional activation.
• The proposed model of the activation complex, involving cII, alphaCTD, and sigma, is supported by existing genetic data.