Cellular DNA Ligase I Is Recruited to Cytoplasmic Vaccinia Virus Factories and Masks the Role of the Vaccinia Ligase in Viral DNA Replication

Abstract

SUMMARY Vaccinia virus (VACV) encodes DNA polymerase and additional proteins that enable cytoplasmic replication. We confirmed the ability of VACV DNA ligase mutants to replicate and tested the hypothesis that cellular ligases compensate for loss of viral gene expression. Knock-down of human DNA ligase I but not other ligases with siRNA or a specific inhibitor severely reduced replication of viral DNA in cells infected with VACV ligase-deficient mutants, indicating that the cellular enzyme plays a complementary role. Replication of ligase-deficient VACV was greatly reduced and delayed in resting primary cells, correlating with initial low levels of ligase I and subsequent viral induction and localization of ligase I in virus factories. These studies indicate that DNA ligation is essential for poxvirus replication and explain the ability of ligase deletion mutants to replicate in dividing cells but exhibit decreased pathogenicity in mice. Encoding of a ligase might allow VACV to “jump-start” DNA synthesis.

Triad of human cellular proteins, IRF2, FAM111A, and RFC3, restrict replication of orthopoxvirus SPI-1 host-range mutants

“…Nevertheless, that result relates to our current finding that the cellular DNA replication proteins FAM111A and RFC are host factors that restrict replication of the SPI-1 mutant. Thus far, investigations of poxvirus DNA replication have focused on viral proteins, except to show that cellular topoisomerase II is recruited by the viral DNA ligase to sites of viral DNA replication (30) and that cellular DNA ligase 1 can substitute for the viral ligase (29). At this time we can only suggest a speculative model for the roles of SPI-1, IRF2, FAM111A, and RFC3 in host restriction of poxviruses that may be useful for designing further studies (Fig.…”

“…Barrier-to-autointegration factor is an example of a host DNA-binding protein that inhibits VACV replication unless inactivated by the poxvirus B1 kinase (28). No cellular proteins essential for poxvirus DNA replication have been identified, although DNA ligase 1 can substitute for the VACV DNA ligase (29) and topoisomerase II is recruited to sites of viral DNA replication (30).…”

Human genome-wide RNAi screen reveals a role for nuclear pore proteins in poxvirus morphogenesis

“…Although a genome-wide RNAi screen of poxvirus replication had not yet been performed, studies with selected siRNAs demonstrated roles for host proteins involved in vaccinia virus (VACV) entry, DNA replication, gene expression, virion assembly, and intracellular transport in mammalian cells (9)(10)(11)(12)(13)(14)(15)(16)(17). Moser et al (18) determined the effects of siRNAs to 440 genes, composing the "kinome," on VACV gene expression in Drosophila cells, and found that the AMP-activated protein kinase pathway plays a major role in VACV entry.…”

Repair of Viral Genomes by Base Excision Pathways: African Swine Fever Virus as a Paradigm

“…Interestingly, many viruses belonging to NCLDVs lack any ligase gene (Yutin and Koonin 2009). It is likely that ligase loss is counteracted by the host protein, as has been demonstrated for vaccinia virus and cellular DNA ligase I (Paran et al 2009). Recombinant purified protein pNP419L has been shown to be a proficient ligase for DNA nicks (Lamarche et al 2005).…”