| Summary: | <p>Abstract</p> <p>Background</p> <p>Epstein-Barr virus is replicated once per cell-cycle, and partitioned equally in latently infected cells. Both these processes require a single viral <it>cis-</it>element, termed <it>oriP</it>, and a single viral protein, EBNA1. EBNA1 binds two clusters of binding sites in <it>oriP</it>, termed the dyad symmetry element (DS) and the family of repeats (FR), which function as a replication element and partitioning element respectively. Wild-type FR contains 20 binding sites for EBNA1.</p> <p>Results</p> <p>We, and others, have determined previously that decreasing the number of EBNA1-binding sites in FR increases the efficiency with which <it>oriP</it>-plasmids are replicated. Here we demonstrate that the wild-type number of binding sites in FR impedes the migration of replication and transcription forks. Further, splitting FR into two widely separated sets of ten binding sites causes a ten-fold increase in the efficiency with which <it>oriP</it>-plasmids are established in cells expressing EBNA1. We have also determined that EBNA1 bound to FR impairs the migration of transcription forks in a manner dependent on the number of EBNA1-binding sites in FR.</p> <p>Conclusion</p> <p>We conclude that EBNA1 bound to FR regulates the replication of <it>oriP</it>-plasmids by impeding the migration of replication forks. Upon binding FR, EBNA1 also blocks the migration of transcription forks. Thus, in addition to regulating <it>oriP </it>replication, EBNA1 bound to FR also decreases the probability of detrimental collisions between two opposing replication forks, or between a transcription fork and a replication fork.</p>
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