Deletions of the Terminal Sequences in the Genomes of the White Pock (u) and Host-restricted (p) Mutants of Rabbitpox Virus

Abstract

The DNA of wild-type rabbitpox virus (u+ .cntdot. p+), and selected u (white pock, u .cntdot. p+) and p (white pock, PK-I5 [pig kidney] cell non-permissive, u .cntdot. p) mutants were compared by restriction enzyme analysis. The cleavage fragments produced by digestion with HindIII or EcoRI endonucleases were separated by agarose gel electrophoresis. Deletions of about 10 .times. 106 were recognized at the right-hand terminus of each u mutant (3 isolates); deletions of 5 .times. 106 to 20 .times. 106 were detected at the left-hand terminus of each p mutant (9 isolates). Rapidly renaturing terminal restriction fragments, indicative of the covalent cross-links, were only found at the terminus unaffected by deleted sequences. Recombinant viruses that were wild-type in genetic characters and in restriction pattern were recovered from mixed infections involving u and p mutants, but no genetic interaction was detected between crosses involving only u or p mutants. The p mutants were divided into 2 non-permissive classes dependent on their biochemical expression in PK-I5 cells: the early class which failed to replicate virus DNA and synthesized only the early polypeptides and the late class which appeared to be normal in virus DNA and polypeptide synthesis. There was no correlation between the extent of the left-hand terminal deletion and the extent of permissiveness of the p mutants in PK-I5 cells.