High dosage Rhp51 suppression of the MMS sensitivity of DNA structure checkpoint mutants reveals a relationship between Crb2 and Rhp51.

BACKGROUND

In eukaryotic cells DNA structure checkpoints organize the cellular responses of DNA repair and transient cell cycle arrest and thereby ensure genomic stability. To investigate the exact role of crb2+ in the DNA damage checkpoint response, a genetic screen was carried out in order to identify suppressors of the conditional MMS sensitivity of a crb2-1 mutant. Here we report the isolation of rhp51+ as a multicopy suppressor.

RESULTS

We show that suppression is not specific for the checkpoint mutant while it is specific for the MMS treatment. Rescue by rhp51+ over-expression is not a consequence of increased recombination repair or checkpoint compensation and epistasis analysis confirms that crb2+ and rhp51+ function in different pathways. A tight linkage between the two pathways is nevertheless suggested by the complementary expression or modification of Crb2 and Rhp51 proteins. Crb2 protein stability is down-regulated when Rhp51 is over-expressed and up-regulated in the absence of Rhp51. The up-regulation of Crb2 is independent of the activation of DNA structure checkpoints. Conversely Rhp51 is more readily activated and differentially modified in the absence of Crb2 or other checkpoint proteins.

CONCLUSIONS

We conclude that fission yeast Crb2 and Rhp51 function in two parallel, tightly connected and coordinately regulated pathways.