Genome of infectious bronchitis virus

Abstract

Techniques are described for the growth and rapid purification of the avian coronavirus infectious bronchitis virus (IBV). Purified IBV has a sedimentation coefficient of 320S and a buoyant density of 1.22 g/ml in sucrose-deuterium oxide equilibrium gradients. IBV RNA extracted by proteinase K in the presence of sodium dodecyl sulfate and further purified by phenol extraction and gradient centrifugation is single stranded and has a sedimentation coefficient of 64S, as determined by isokinetic gradient centrifugation. Analysis on sucrose gradients under both aqueous and denaturing conditions together with agarose gel electrophoresis in the presence of the chaotropic agent methylmercuric hydroxide gave a value of 8 X 10(6) for the moleclar weight of IBV RNA. This value was confirmed by RNase T1 fingerprinting, which also indicated that IBV RNA is haploid. No evidence was found of subunit structure in IBV RNA. From these results together with the recently reported observation that IBV RNA is infectious and contains a tract of polyadenylic acid (Lomniczi, J. Gen. Virol., in press), we conclude that the genome of the coronaviruses is a single continuous chain of about 23,000 mononucleotides that is of messenger polarity.