Loss of activities for mRNA synthesis accompanies loss of lambda2 spikes from reovirus cores: an effect of lambda2 on...

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• The reovirus lambda2 protein is a key component of the viral core particle.
• Lambda2 is known to catalyze essential enzymatic activities for 5' cap 1 structure formation on viral RNA transcripts.
• Limited evidence suggests lambda2 may also be involved in viral transcription.

Purpose of the Study:

• To investigate the roles of reovirus lambda2 protein in core functions beyond RNA capping.
• To understand the structural and functional requirements of lambda2 in viral transcription and other enzymatic activities.

Main Methods:

• Reovirus cores were treated with heat, protease, and detergent to generate lambda2-depleted particles ('spikeless cores').
• Transmission cryo-electron microscopy (cryo-TEM) and scanning cryo-electron microscopy were used to analyze particle structure.
• Functional assays were performed to assess RNA capping, transcription, and nucleoside triphosphate hydrolysis activities.

Main Results:

• Spikeless cores, depleted of lambda2, retained other core proteins and genome segments but lost lambda2 spikes.
• These spikeless cores exhibited significantly reduced RNA capping, transcription, and nucleoside triphosphate hydrolysis activities.
• Cryo-TEM and 3D image reconstruction revealed structural changes in the core shell (lambda1) upon lambda2 loss, including the elimination of pores near fivefold axes.

Conclusions:

• Reovirus lambda2 protein plays critical roles in viral RNA capping, transcription, and nucleoside triphosphate hydrolysis.
• The structural integrity of the reovirus core, particularly the lambda1 shell, is influenced by the presence of lambda2.
• Changes in the core shell structure upon lambda2 loss may underlie the observed reductions in transcriptase-related activities.