The white pock (μ) mutants of rabbit poxvirus. III. Terminal DNA sequence duplication and transposition in rabbit poxvirus

The restriction fragment patterns of the DNA of three white pock (μ) nonhost range mutants (RPμ mutants) of rabbit poxvirus (RPV) show the presence of net insertions of DNA. Two of the mutants (RPμ21 and RPμ7) contain two molar quantities of 13 × 10 6 and 15 × 10 6 daltons, respectively, of the left-most viral DNA sequences. The extra copy of these sequences was inserted into the right-most region of the viral genome which in both cases had been modified by deletion of 10 × 10 6 daltons of the original extreme right-most DNA sequences. Hence two mutants with “left-hand” mirror image termini of 13 × 10 6 and 15 × 10 6 daltons of DNA were generated with an overall net increase in mass of 3 × 10 6 and 5 × 10 6 daltons of DNA to yield genome molecular weights of 121 × 10 6 and 123 × 10 6 for RPμ21 and 7, respectively. A third mutant (RPμ81g) contained 28 × 10 6 daltons of the right-most parental DNA sequences inserted into the left end of the genome, which had deleted 6 × 10 6 daltons of the extreme left-hand sequences. This variant contains “right-hand” mirror image termini of 28 × 10 6 daltons of DNA and a net increase in molecular weight of 22 × 10 6 daltons of DNA to yield a genome molecular weight of 140 × 10 6. The cross-linked end of the transposed sequences is retained in all cases. Our data suggest that the terminal DNA sequences at either end of the virus are not essential for a productive infection in certain host cells and that the pathogenecity of orthopox-viruses may be related in part to a series of varied and interchangeable DNA sequences located at both extremes of a highly conserved genome core.