Stn1, a new Saccharomyces cerevisiae protein, is implicated in telomere size regulation in association with Cdc13.

Abstract

We have isolated STNl, an essential Saccbaromyces cerevisiae gene, as a suppressor of the cdcl3-l mutation. A synthetic lethal interaction between a temperature-sensitive mutant allele of STNl, stnl-13, and cdcl3-l was observed. Stnl and Cdcl3 proteins displayed a physical interaction by two-hybrid analysis. As shown previously for cdcl3-l, stnl-13 cells at the restrictive temperature accumulate single-stranded DNA in subtelomeric regions of the chromosomes, but to a lesser extent than cdcl3-l cells. In addition, both Cdcl3 and Stnl were found to be involved in the regulation of telomere length, mutations in STNl or CDC13 conferring an increase in telomere size. Loss of Stnl function activated the RAD9 and MEC3 G2/M checkpoints, therefore confirming that DNA damage is generated. We propose that Stnl functions in telomere metabolism during late S phase in cooperation with Cdcl3.

Pol12, the B subunit of DNA polymerase α, functions in both telomere capping and length regulation

“…Three other mutants that showed an elongated telomere phenotype were identified by direct plasmid complementation and segregation analysis as alleles of either RIF1 (M56 and M174) or STN1 (M3; data not shown). Both of these genes have been shown previously to be involved in telomere length regulation, and, in the case of STN1, in an essential telomere protection function (Hardy et al 1992;Grandin et al 1997).…”

“…A temperature-sensitive allele of STN1, stn1-13, confers a phenotype very similar to that displayed by cdc13-1 cells, causing G2/M cell cycle arrest and accumulation of telomeric single-stranded DNA at the nonpermissive temperature. In addition, both mutations lead to telomere length increase at the semipermissive temperature (Grandin et al 1997).…”

“…In any event, mutants lacking this Cdc13 function (e.g., cdc13-2) senesce because of gradual telomere erosion (Lendvay et al 1996;Nugent et al 1996), whereas complete loss of Cdc13 activity leads to extensive degradation of telomeric 5Ј-ends and an immediate G2/M cell cycle arrest. This essential capping function of Cdc13, which is lost in the conditional-lethal cdc13-1 allele when grown at the nonpermissive temperature (Garvik et al 1995), involves the delivery of a separate complex to the telomere, containing Stn1 and Ten1 (Grandin et al 1997(Grandin et al , 2001Pennock et al 2001). A temperature-sensitive allele of STN1, stn1-13, confers a phenotype very similar to that displayed by cdc13-1 cells, causing G2/M cell cycle arrest and accumulation of telomeric single-stranded DNA at the nonpermissive temperature.…”

The U3 small nucleolar ribonucleoprotein component Imp4p is a telomeric DNA-binding protein

“…The Cdc13p-mediated telosomic complex contains proteins including Stn1p, Ten1p, Est1p, Pol1p, Zds2p, Sir4p and Imp4p [11,12,14,15]. Imp4p was identified from yeast two-hybrid screening experiments using Cdc13p as the bait.…”

“…In S. cerevisiae, Rap1p binds to the doublestranded telomeric DNA and Cdc13p binds specifically to the single-stranded portion of the telomeres [7][8][9][10]. These two proteins serve as a core for other proteins to form a multiple protein-DNA complex in telomeres [11][12][13][14][15]. Together they participate in multiple functions on telomeres, such as end protection and replication.…”