Previous work has shown that NA has a tendency to cluster at one of the poles of influenza filaments; however, while tomograms of Udorn virions suggested that NA clusters at the end of the virion opposite to the end where the RNPs are attached [21], a recent analysis using high-throughput fluorescence microscopy to visualize endogenously labelled NA within filaments revealed a tendency for NA to colocalize with NP, in turn suggesting that NA localization is linked to the location of the viral genome [14]. The gene discussed is XK; the disease is influenza.