DNA-damaging enediyne C-1027 inhibits initiation of intracellular SV40 DNA replication in trans

This study used 2-D agarose gel techniques to examine the effects of the DNA-strand scission enediyne C-1027 on DNA replication in SV40-infected BSC-1 cells. Replication of SV40 DNA was inhibited by C-1027 to a greater extent than was BSC-1 genomic DNA replication in infected cells. Low nanomolar concentrations (0.2-10 nM) of C-1027 affected a rapid, progressive decrease in SV40 replication activity and replication intermediates (RIs) within 15 min after drug addition. A concurrent decrease in the signal of both the SV40 bubble arc and replication activity with increasing concentrations of C-1027 suggested that C-1027 inhibited initiation of new RIs. Additionally, the reduction in bubble arc signal observed with C-1027 was prevented when elongation of nascent chains was blocked by aphidicolin. Thus, the C-1027-induced disappearance of RIs probably is related to the maturation of preformed replication molecules in the absence of initiation of new RIs. Strand damage to SV40 DNA was barely detectable at concentrations where inhibition of replication activity was nearly complete, indicating that C-1027 replication inhibition occurs in trans.