A tel2 Mutation That Destabilizes the Tel2-Tti1-Tti2 Complex Eliminates Rad3^ATR Kinase Signaling in the DNA Replication Checkpoint and Leads to Telomere Shortening in Fission Yeast

ABSTRACT

In response to perturbed DNA replication, ATR (ataxia telangiectasia and Rad3-related) kinase is activated to initiate the checkpoint signaling necessary for maintaining genome integrity and cell survival. To better understand the signaling mechanism, we carried out a large-scale genetic screen in fission yeast looking for mutants with enhanced sensitivity to hydroxyurea. From a collection of ∼370 primary mutants, we found a few mutants in which Rad3 (ATR ortholog)-mediated phospho-signaling was significantly compromised. One such mutant carried an uncharacterized mutation in tel2, a gene encoding an essential and highly conserved eukaryotic protein. Previous studies in various biological models have shown that Tel2 mainly functions in Tel2-Tti1-Tti2 (TTT) complex that regulates the steady-state levels of all phosphatidylinositol 3-kinase-like protein kinases, including ATR. We show here that although the levels of Rad3 and Rad3-mediated phospho-signaling in DNA damage checkpoint were moderately reduced in the tel2 mutant, the phospho-signaling in the DNA replication checkpoint was almost completely eliminated. In addition, the tel2 mutation caused telomere shortening. Since the interactions of Tel2 with Tti1 and Tti2 were significantly weakened by the mutation, destabilization of the TTT complex likely contributes to the observed checkpoint and telomere defects.

KEYWORDS:

• ATR
• Cds1
• Chk1
• Rad3
• Tel2
• genome integrity
• hydroxyurea
• replication checkpoint
• replication stress
• telomere

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at https://doi.org/10.1128/MCB.00175-19.

ACKNOWLEDGMENTS

We thank Tom Kelly and Paul Russell for sharing the yeast strains, Nancy Walworth for Chk1 phospho-specific antibody, and Michael Kemp and three anonymous reviewers for critical reading of the manuscript. Other members of the Xu lab are acknowledged for their help and support.

This study was supported by NIH RO1 grants GM110132 to Y.J.X. and GM078253 to T.M.N.