An intermediate state allows influenza polymerase to switch smoothly between transcription and replication cycles

Area of Science:

• Virology
• Structural Biology
• Molecular Mechanisms

Background:

• Influenza polymerase (FluPol) orchestrates viral mRNA transcription and genome replication.
• The mechanism of FluPol's functional switching between transcription and replication states remains unclear.
• Distinct structural conformations underlie FluPol's transcription and replication activities.

Purpose of the Study:

• To elucidate the mechanism by which FluPol switches between transcription and replication states.
• To characterize a previously unstudied conformation of FluPol involved in functional switching.
• To investigate the role of this novel conformation in regulating viral life cycle activities.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the structure of H5N1 FluPol.
• High-resolution structural analysis (3.7 Å) of the intermediate state was performed.
• Functional assays were conducted to assess the necessity of the intermediate state for FluPol activity.

Main Results:

• A novel 'intermediate state' conformation of H5N1 FluPol was identified and structurally characterized.
• This intermediate state features a blocked cap-binding domain and a contracted core region.
• The formation of the intermediate state is demonstrated to be critical for both transcription and replication activities of FluPol.

Conclusions:

• A mechanism for FluPol functional switching through an intermediate state is proposed.
• The intermediate state facilitates smooth transitions into either transcription or replication states.
• The transcription and replication cycles of Influenza polymerase are regulated via this essential intermediate state.