Yra1 is required for S phase entry and affects Dia2 binding to replication origins

The Saccharomyces cerevisiae F-box protein Dia2 is important for DNA replication and genomic stability. Using an affinity approach, we identified Yra1, a transcription-coupled mRNA export protein, as a Dia2 interaction partner. We find that yra1 mutants are sensitive to DIA2 expression levels. Like Dia2, Yra1 associates with chromatin and binds replication origins, suggesting that they may function together in DNA replication. Consistent with this idea, Yra1 and Dia2 coimmunoprecipitate with Hys2, a subunit of DNA polymerase δ. The C terminus of Yra1 is required to interact with Dia2. A yra1 mutant that lacks this domain is temperature sensitive yet has no apparent defect in RNA export. Remarkably, this mutant also fails to enter S phase at the nonpermissive temperature. Significantly, other mutants in transcription-coupled export do not exhibit S phase entry defects or sensitivity to DIA2 expression levels. Together, these results indicate that Yra1 has a role in DNA replication distinct from its role in mRNA export. Furthermore, Dia2 binding to replication origins is significantly reduced when association with Yra1 is compromised, suggesting that one aspect of the role of Yra1 in DNA replication may involve recruiting Dia2 to chromatin.