The Polypeptide Composition of Avian Infectious Bronchitis Virus Particles

Summary Egg grown avian infectious bronchitis virus (IBV) centrifuged on sucrose density gradients was found to consist of a major virus peak of density 1.17 to 1.18 g/cm 3 and occasionally two minor virus peaks of density 1.21 to 1.22 g/cm 3 and 1.13 g/cmd. Three different IBV strains were examined and no morphological differences were detected between virus particles of different densities or from different strains. The polypeptides of the different density virus particles from the three IBV strains were analysed on polyaerylamide gels. In all cases 7 polypeptides were observed, although there were differences in the proportions of these polypeptides in particles of different densities and those from the different strains. The polypeptides have been called VP 1 (molecular weight 130,000), VP 2 (105,000), VP3 (97,000), VP4 (8t,000), VP5 (74,000), VP6 (51,000) and VP7 (33,000). Additional polypeptides were produced if slightly harsher treatments were used.