Novobiocin inhibition of simian virus 40 DNA replication

Abstract

Supercoiling in eukaryotic cells can be explained by the packaging of DNA into nucleosomes in the presence of nicking–closing enzymes¹. This does not, however, rule out the presence of a DNA gyrase. DNA gyrase² is involved in the introduction and maintenance of supercoiling in prokaryotic cells^3–6 and in DNA replication in Escherichia coli^4,6,7. Novobiocin and coumermycin-A₁ inhibit prokaryotic DNA replication^4,7–11 by inhibiting the subunit of the gyrase responsible for its ATPase and energy transduction activities^3,4,12–14. The inhibition of DNA synthesis in a mammalian cell¹⁵ and in rat liver mitochondria¹⁶ by novobiocin suggests that a gyrase required for initiation of replication is inhibited. Because the presence of a gyrase in eukaryotic cells would be of great interest, I have examined this question in a well characterized model system, the replication of simian virus 40 in its host (monkey) cell. The results demonstrate here that novobiocin and coumermycin A₁ inhibit SV40 DNA synthesis in mammalian cells and inhibit DNA polymerase α, the replicative DNA polymerase in this system^17,18. Novobiocin, but not coumermycin A₁, reduces the degree of supercoiling of DNA pulse-labelled in its presence, probably through its inhibition of protein synthesis. Thus the inhibition of SV40 DNA synthesis by novobiocin does not alone prove the involvement of a DNA gyrase.