Genetic complementation reveals structure-function links in nodavirus RNA replication complex crowns

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Positive-strand RNA viruses utilize virus-induced organelles for RNA genome replication.
• Nodaviruses feature cytosolic "crown" complexes of viral RNA replication proteins (protein A) that manage RNA synthesis, capping, and release.

Purpose of the Study:

• To investigate the functional roles and cooperative interactions of protein A in viral RNA replication.
• To elucidate the contributions of different protein A conformations and domains to replication processes.

Main Methods:

• Utilized mutational analysis, complementation assays, and functional studies.
• Investigated the impact of deletions and mutations in protein A's polymerase and capping domains.

Main Results:

• Protein A's polymerase and RNA capping active sites function independently in distinct protein A copies.
• Certain RNA capping steps require the same protein A subunit, while others do not.
• Structural integrity, not just enzymatic activity, is crucial for crown assembly and function.
• The intrinsically disordered C-terminal region of protein A is surprisingly critical for RNA replication efficiency.

Conclusions:

• Protein A functions through a cooperative and interdependent mechanism involving multiple conformations and subunits.
• Distinct protein A copies specialize in specific functions like RNA synthesis or capping.
• The structural integrity and specific domains of protein A are essential for efficient viral RNA replication.