A hidden gene in astroviruses encodes a cell-permeabilizing protein involved in virus release

Valeria Lulla; Andrew E. Firth

To determine which stage of the virus replication cycle is affected in XP knock-out viruses, we quantified released virus and viral protein and RNA levels for BSR cells electroporated with in vitro transcribed full-length pAVIC1 T7 RNAs. As expected, neither RNA nor protein levels were affected in cell-derived samples (Fig. 4G ). In contrast, in media-derived samples, XP mutant titers were significantly below wt titers when analyzed by qRT-PCR (fold differences = 0.08 and 0.05, p = 0.002 and 0.003 for AUG vs wt and PTC vs wt respectively; 2-tailed t-tests with separate variances) or virus titration (Fig. 4G ). These analyses indicate the involvement of XP late in the virus replication cycle, with XP potentially acting in either virus assembly or virus release. Since previous structural studies on the HAstV CP 20 and virion 21 have not indicated the presence of any additional proteins in the compact 43-nm virion structure, the more likely role for XP is in virus release.