The measles virus nucleocapsid protein tail domain is dispensable for viral polymerase recruitment and activity

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Paramyxovirus genomes form ribonucleoprotein (RNP) complexes with nucleoprotein (N)-encapsidated viral RNA.
• Measles virus (MeV) N protein has an RNA-binding core and a tail domain, crucial for polymerase complex recruitment via phosphoprotein (P) interaction.
• The P-N tail interaction is critical for polymerase complex recruitment to the viral RNA template.

Purpose of the Study:

• To investigate the role of the MeV N protein tail domain in RNP bioactivity and polymerase complex function.
• To engineer MeV N variants with progressively truncated tail domains to assess their impact on RNP template activity.
• To elucidate the mechanism of polymerase recruitment and template engagement during MeV replication.

Main Methods:

• Engineering of MeV N variants with systematic tail truncations.
• Assessment of RNP bioactivity using polymerase template assays.
• Analysis of polymerase recruitment and activity with modified N proteins and phosphoproteins.
• Investigating the effect of inserting tags into the N-tail on RNP bioactivity.

Main Results:

• N truncations lacking the C-terminal 43 residues (including the MoRE domain) abolish RNP template activity.
• Removing surface-exposed N-tail residues significantly restores RNP bioactivity, independent of sequence.
• Insertion of dominant tags in the N-tail reduces bioactivity, indicating a negative regulatory role for exposed N-tail segments.
• While N-MoRE binding to P is dispensable for polymerase recruitment, it stabilizes the polymerase-RNP complex and facilitates template access.

Conclusions:

• MeV polymerase can directly dock to the nucleocapsid core, challenging existing replication models.
• The N-tail's exposed segments negatively regulate RNP bioactivity, while the MoRE domain interaction with P stabilizes the polymerase complex.
• These findings provide a revised understanding of MeV replication, highlighting the dynamic role of the N-tail in polymerase recruitment and function.