In previous work, we identified Stn1 as an additional
protein connected to the budding yeast S phase checkpoint
(Gasparyan et al. 2009). Stn1 was initially identified as a
component of the conserved Cdc13–Stn1–Ten1 (CST) complex (Grandin et al. 1997; Rice and Skordalakes 2016). In
yeast, CST binds telomere DNA repeats and protects chromosome ends from exonuclease digestion during S phase
(Garvik et al. 1995; Nugent et al. 1996; Lin and Zakian
1996; Maringele and Lydall 2002; Jia et al. 2004; Bertuch
and Lundblad 2004; Zubko and Lydall 2006; Vodenicharov and Wellinger 2006; Xu et al. 2009; Dewar and Lydall 2012; Langston et al. 2020). Yeast Stn1 also binds the
Pol12 subunit of the DNA polymerase α/DNA primase
complex (Polα; Grossi et al. 2004; Petreaca et al. 2006).
The Stn1–Polα interaction plays a conserved role in chromosome end replication by stimulating Polα priming and fill-in
synthesis of telomerase-generated ssDNA overhangs (Qi and
Zakian 2000; Grossi et al. 2004; Petreaca et al. 2007; Puglisi
et al. 2008; Chen and Lingner 2013). Importantly, however,
other observations implicate CST in genome-wide aspects
of DNA replication, particularly under conditions of DNA
replication stress (Stewart et al. 2018). In a previous publication, we showed STN1 overproduction (STN1 OP) causes
yeast cells to become extremely sensitive to HU and other
replication stressors (Gasparyan et al. 2009). Remarkably,
STN1 OP also phenocopies rad53 S phase checkpoint defects
in HU, including activation of later-firing, Rad53-checked
ORIs and premature spindle extension. Rad53 is activated
normally in STN1 OP cells, indicating upstream events in S
phase checkpoint signaling are not perturbed by excess Stn1.
While this suggests STN1 OP acts downstream or in parallel
to Rad53 to antagonize checkpoint effector responses, the
underlying mechanisms remain to be defined.

### Language ###
English

### Assessment ###
We can ask about the role of Stn1 in DNA replication stress, which is a clear piece of information from the text.

### Query ###
What role does Stn1 play during DNA replication stress?
What role does Stn1 play during DNA replication stress?