Avian Reovirus Morphogenesis Occurs Within Viral Factories and Begins with the Selective Recruitment of σNS and λA to μNS Inclusions

We have recently shown that the avian reovirus non-structural protein μNS forms cytoplasmic inclusions in transfected cells and recruits σNS to these structures. In the present study we further demonstrate that μNS mediates the association of the major core protein λA, but not of σA or σC, with inclusions, indicating that the recruitment of viral proteins into avian reovirus factories has specificity. Thus, some proteins appear to be initially recruited to factories by association with μNS, whereas others are recruited subsequently through interaction with as-yet-unknown factors. We next used metabolic pulse-chase radiolabeling combined with cell fractionation and antibody immunoprecipitation to study the recruitment of newly synthesized viral polypeptides into viral factories and virus particles. The results of this combined approach revealed that avian reovirus morphogenesis is a complex and temporally controlled process that takes place exclusively within globular viral factories that are not microtubule-associated. Our findings further suggest that cores are assembled within the first 30 minutes after the synthesis of their polypeptide components, and that reovirion morphogenesis is completed over the next 30 minutes by the subsequent addition of outer capsid proteins.