DNA replication and telomere resolution in vaccinia virus

Abstract

A drug resistant mutant was isolated and mapped to the vaccinia virus encoded DNA ligase gene. Three independent mutants were sequenced and each had a single point mutation. Pulsed-field gel electrophoresis (PFGE) along with restriction enzyme digestion and Southern blot analysis also demonstrate that the addition of etoposide to cells infected with the vaccinia virus strain WR29, a plaque purified isolate from strain WR with several sets of the NR2/tandem repeat sequence, strongly inhibit d replication of the viral genome. Interestingly, a 1.6-Kb fragment which contains the NR2 and tandem repeat sequences was present in large amounts and had apparently been selectively amplified. Transfection of the plasmid which contains this 1.6-Kb sequence into vaccinia WR-infected rabbit cornea (SIRC) cells indicated that plasmid replication in these cells is not inhibited under conditions where replication of the viral DNA genome is strongly suppressed. Using pulsed-field gel electrophoresis (PFGE) along with restriction enzyme analysis, the vaccinia virus conditional lethal temperature-sensitive mutant ts793 was demonstrated to be defective in telomere resolution at the non-permissive temperature (40$\sp\circ$C). It has the same phenotype as another ts mutant, ts9383 (Carpenter and DeLange, 1991). Each of the ts mutants had a single point mutation in the virus-encoded mRNA capping enzyme. Mutant ts9383 has been mapped to the small subunit of the mRNA capping enzyme (D12) and ts793 to the large subunit of the mRNA capping enzyme (D1). RNA analysis indicated that one of the late promoters which was located in NR1, the unique region distal to the tandem repeats, was poorly utilized by these two ts mutants at 40$\sp\circ$C. (Abstract shortened by UMI.)