The histone-interacting domain of nuclear factor I activates simian virus 40 DNA replication in vivo

Efficient initiation of SV40 DNA replication requires transcription factors that bind auxiliary sequences Banking the minimally required origin. To ev aluate the possibility that transcription factors may activate SV40 replica tion by acting on the chromatin structure of the origin, we used an in vivo replication system in which we targeted GAL4 fusion proteins to the minima lly required origin. We found that the proline-rich transcriptional activat ion domain of nuclear factor I (NF-I), which has been previously shown to i nteract with histone H3, specifically activates replication. Evaluation of a series of deletion and point mutants of NF-I indicates that the H3-bindin g domain and the replication activity coincide perfectly. Assays with other transcription factors, such as Spl, confirmed the correlation between the interaction with H3 and the activation of replication. These findings imply that transcription factors such as NF-I can activate SV40 replication via direct interaction with chromatin components, thereby contributing to the r elief of nucleosomal repression at the SV40 origin.