DNA Replication Efficiency Depends on Transcription Factor-Binding Sites

Naturally arising variants of simian virus 40 (SV40), generated by serial passage of the virus at high multiplicities of infection, provide important insight into the role of transcription factor-binding sites in enhancing DNA replication. Although the variants that arise from numerous recombination events are the result of selective pressure to replicate more efficiently than the other variants in the infection, there is no transcription pressure. Therefore, it is interesting that a minimum of two viral Sp1 transcription factor-binding sites are retained and that host AP-1 and NF-1 transcription factor-binding sites are incorporated into the 100-bp regulatory region that maximizes DNA replication in these variants. We cotransfected COS-1 cells (that provide viral large T antigen for DNA replication) to examine the effect of transcription factor-binding sites on the replication of plasmid constructs that contain the SV40 origin of replication (ori). The level of relative replication efficiency (RRE) depends on the number and type of transcription factor-binding sites. Replication increases as the number of transcription factor-binding sites increases within the regulatory region of the variants; AP-1 sites are more effective than NF-1 transcription factor-binding sites. Competition between constructs in transfections magnifies the difference in their RREs. The results indicate that transcription factor-binding sites play an important role in enhancing DNA replication.