Phosphorylation of highly conserved serine residues in the influenza A virus nuclear export protein NEP plays a minor role in viral growth in human cells and mice.

Phosphorylation at the highly conserved serine residues S23 to S25 in the nuclear export protein (NEP) of influenza A viruses was suspected to regulate its nuclear export activity or polymerase activity-enhancing function. Mutation of these phosphoacceptor sites to either alanine or aspartic acid showed only a minor effect on both activities but revealed the presence of other phosphoacceptor sites that might be involved in regulating NEP activity.