A regulatory phosphosite on Mec1 controls RNAPII and RNAPIII occupancy during replication stress [ChIP-seq]

Upon replication stress, the Mec1ATR kinase triggers the downregulation of transcription, reducing the level of RNA polymerase on chromatin to facilitate replication fork progression. We identify a hydroxyurea-induced phosphorylation site at Mec1-S1991 that contributes to the eviction of RNAPII and RNAPIII during replication stress. The non-phosphorylatable mec1-S1991A mutant reduces replication fork progression genome-wide and compromises survival on hydroxyurea. This defect can be suppressed by destabilizing chromatin-bound RNAPII with a Rpb3-TAP fusion, suggesting that lethality arises from replication-transcription conflicts. Coincident with a failure to repress gene expression, highly transcribed genes like GAL1 persist at nuclear pores in mec1-S1991A cells. Consistently, we find pore proteins and several components controlling RNAPII and RNAPIII transcription are phosphorylated in a Mec1-dependent manner, suggesting that Mec1-S1991 phosphorylation limits conflicts between replication and either RNA polymerase complex. We further show that Mec1 contributes to reduced RNAPII occupancy on chromatin during an unperturbed S phase. Overall design: Pol2 genome-wide profiling during DNA replication stress in wt-cells and mec1 mutants