# Regulatory hotspot on the influenza A virus polymerase revealed through the structure of the NEP-polymerase complex

## TL;DR

This study reveals how the influenza virus regulates its replication and RNA export through a key protein interaction.

## Contribution

The paper identifies a regulatory hotspot on the influenza A virus polymerase through a high-resolution NEP-polymerase complex structure.

## Key findings

- NEP binds to the IAV polymerase at a site overlapping with host factors, acting as a regulatory hotspot.
- NEP alone can promote vRNP export, with the matrix protein 1 enhancing this process.
- The NEP-polymerase interaction coordinates transitions between RNA synthesis and nuclear export.

## Abstract

Influenza A virus (IAV) transcribes and replicates its segmented RNA genome in the host nucleus within viral ribonucleoproteins (vRNPs), which are exported for virion assembly. The nuclear export protein (NEP) is essential for this process and also regulates viral RNA synthesis, implicating a direct interaction with the viral RNA polymerase. Here, we present a 2.5-Å cryogenic electron microscopy structure of NEP bound to the IAV polymerase and demonstrate that NEP alone is sufficient to promote vRNP export, with the viral matrix protein 1 enhancing export efficiency. NEP forms a four-helix bundle that binds at the interface of the PA C-terminal domain and PB1 N terminus of the polymerase. The NEP binding site at this interface overlaps with those for the host ANP32 and the C-terminal domain of RNA polymerase II, indicating that it functions as a regulatory hotspot coordinating transitions of the viral polymerase between RNA synthesis and nuclear export, revealing a critical layer of control in the IAV replication cycle.

Structural studies reveal how influenza virus switches between making new RNA genomes and exporting them from the host nucleus.