The possible roles for polyamines in the initiation process of SV40 DNA replication in vitro.

The polyamines are aliphatic cations which are present in millimolar concentrations in all mammalian cells, and are required for optimal growth of almost all cell types. In this study, the roles of polyamines in DNA replication in vitro and the mechanism by which polyamines affected DNA replication were examined using simian virus 40 DNA replication system in vitro. We found that polyamines inhibited DNA replication, but it is not clear at which stage this occurs. Spermidine inhibited the DNA cleavage by topoisomerase I at 8.0 mM, but stimulated its activity at 1.0 mM. Spermine also inhibited its activity at 4.0 mM, but stimulated at 1.0 mM. The ssDNA binding activity of replication protein A was slightly affected by polyamines. Polyamines, especially spermine, also significantly reduced polymerase alpha-primase activity at 133 microM. Taken together, we suggest that the major inhibition of SV40 DNA replication may be due to the inhibition of pol alpha-primase activity, and possible roles for polyamines in the initiation process are discussed.