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We have determined the sequence for 1,000 bases from the 3' terminus of a human astrovirus serotype 1 isolated in Newcastle. This is the first sequence reported for a representative of this virus family. We find one open reading frame which terminates 83 bases from a poly A tail. The 3' non-coding-region has similarities to some picornavirus termini. However the amino acids specified by the coding region have no significant homology to the picornavirus protein 3D, encoded at the 3' terminus of these viruses. Northern blot analysis of intracellular virus-specific RNAs revealed one size of transcript which corresponded to full-length virus RNA. Available data thus indicate that astroviruses may resemble picornaviruses in replication strategy.

Summary We report here the cloning and 3′ sequence determination of feline calicivirus strain F9. Subcloning the 3′ terminus enabled the production of strand specific probes for RNA synthesis. We extend the number of virus specific RNAs detected intracellularly to 8, and show that numbers 1–5 are represented as negative strands which may serve as templates in the synthesis of these RNAs.

The interfering activity of incomplete avian influenza A (fowl plague) virus was titrated using an infectious centre reduction assay. It was found that the interference property had poissonian kinetics only at low multiplicities of infection.

Incomplete influenza A virus (fowl plague Dobson strain) was prepared by undiluted passage in primary chick embryo fibroblast cells. Analysis of released virus RNA revealed a deficiency in RNA segments 1-3, characteristic of incomplete virus formation. The virus yield from a high multiplicity infection with standard virus always showed this deficiency, even when analysed as early as 6 hours post-infection, whereas infection at low multiplicity gave rise to virus indistinguishable in RNA composition from the parent virus. The relative amounts of intracellular, non-polyadenylated, complementary RNA (template RNA) were found to reflect accurately the eventual RNA composition of released virus, and were altered in phase with PFU:HAU ratio, throughout a von Magnus cycle.

Summary We have used Western blotting to examine the accumulation of feline calicivirus proteins within the infected cell. Experiments using elevated growth temperature to block post-translational cleavage have demonstrated two additional high molecular weight protein bands 125 kd and 123 kd respectively which may be precursor polyproteins. Inhibition of proteolytic processing withp-fluorophenylalanine led to the accumulation of several additional protein species which may represent intermediates in the protein processing pathway. None of these proteins were related to the 62 kd major capsid protein (cP 62) of the virus as judged by reaction with monoclonal antibodies. The production of a 76 kd capsid precursor protein (cpP 76) was demonstrated for the first time in FCV-infected cells. The pathway by which calicivirus polypeptides are made thus appears highly complex and may involve temporal regulation of protein synthesis as well as protein processing. Tentative identification of primary, intermediate and mature forms of virus proteins is discussed.

Incomplete avian influenza (fowl plague) virus derived by undiluted egg passage, displayed an increased capacity to promote the synthesis of intracellular virus-specific proteins when compared with standard virus. The in vitro virion-bound RNA polymerase activity of incomplete virus was also greater than could be explained by the presence of residual infectious virus. When the titres of infectious and interfering virus species were determined directly, they did not account for all the virus present. The existence of defective non-interfering (DNI) virus, even in standard virus preparations, was inferred. DNI virus is capable of initiating infection, synthesis of mRNA and proteins but cannot complete a productive replication cycle, and does not interfere with multiplication of standard virus. Such DNI virus could exaggerate the true extent of DI virus formation by lowering the PFU:HAU ratio and so account for the failure to correlate infectivity with RNA composition or RNA polymerase activity.