Influenza virus temperature-sensitive cap (m7GpppNm)-dependent endonuclease

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Influenza viral mRNA synthesis initiates with endonucleolytic cleavage of capped RNAs.
• This process generates short capped primers essential for viral mRNA elongation.

Purpose of the Study:

• To investigate the temperature sensitivity of influenza mRNA synthesis steps.
• To determine the role of the viral PB2 protein in cap recognition and endonuclease activity.

Main Methods:

• Utilized purified wild-type and temperature-sensitive (ts1, ts6) WSN virus cores for in vitro transcription assays.
• Assessed the temperature sensitivity of endonucleolytic cleavage and overall transcription at permissive (33°C) and non-permissive (39.5°C) temperatures.
• Examined cap-dependent primer binding to viral cores.

Main Results:

• Wild-type viral cores showed similar transcription rates at both temperatures.
• Mutant ts1 and ts6 viral cores exhibited significantly reduced cap-dependent endonuclease activity at the non-permissive temperature.
• The temperature-sensitive defect was localized to the cap recognition step of the endonuclease reaction.

Conclusions:

• The viral PB2 protein is essential for recognizing the 5'-terminal cap 1 structure during endonuclease activity.
• Mutations in the PB2 protein specifically impair the cap-dependent endonuclease function, not subsequent transcription steps.
• This study identifies a critical role for PB2 in initiating influenza viral mRNA synthesis through cap recognition.