FIG. 6.

Model for the role of Top3p in mediating S-phase checkpoint responses. We propose that the Sgs1-Top3 complex is involved in the early processing of aberrant structures arising at blocked or stalled replication forks. The complex may play at least two roles: preparation of lesions for repair by the recombinational repair pathway and activation of the checkpoint that leads to an inhibition of cell cycle progression. In the absence of Top3, there is a failure to adequately integrate the cellular response to the disturbance of replication.