Phosphorylation of NEP 1 Phosphorylation of highly conserved serine residues in the influenza A virus nuclear 1 export protein NEP plays a minor role in viral growth in human cells and mice

26 Phosphorylation at the highly conserved serine residues S23 to S25 in NEP of influenza A 27 viruses was suspected to regulate its nuclear export activity or polymerase-activity enhancing 28 function. Mutation of these phosphoacceptor sites to either alanine or aspartic acid showed 29 only a minor effect on both activities, but revealed the presence of other phosphoacceptor 30 sites that might be involved in regulating NEP activity. 31 32