NusA directly interacts with antitermination factor Q from phage λ

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Antitermination (AT) regulates bacterial transcription by suppressing termination signals.
• Phage λ protein Q (λQ) controls late gene expression by interacting with the transcription elongation complex.
• The molecular mechanisms of λQ-dependent AT and its reliance on N-utilization substance (Nus) A are not fully understood.

Purpose of the Study:

• To elucidate the structural basis of phage λ protein Q (λQ).
• To investigate the interaction between λQ and the multidomain protein NusA.
• To understand the role of these interactions in λQ-dependent antitermination.

Main Methods:

• Solution-state nuclear magnetic resonance (NMR) spectroscopy was employed to determine the structure of λQ.
• NMR was used to characterize the interactions between λQ and different domains of NusA.
• Structural and interaction data were analyzed to propose a model for λQ-dependent AT.

Main Results:

• The solution structure of λQ revealed unstructured N-terminal residues.
• NusA directly interacts with λQ via its N-terminal domain (NTD) and acidic repeat 2 (AR2) domain.
• The binding sites on λQ for NusA-NTD and NusA-AR2 overlap and are mutually exclusive, indicating distinct roles.

Conclusions:

• The λQ:NusA-AR2 interaction can release NusA autoinhibition.
• Mutually exclusive interactions suggest distinct functions for NusA domains in AT.
• Repositioning of NusA-NTD by λQ may be a general mechanism for suppressing transcription termination in AT.