Regulation of Telomere Length by Checkpoint Genes inSchizosaccharomyces pombe

Abstract

We have studied telomere length in Schizosaccharomyces pombe strains carrying mutations affecting cell cycle checkpoints, DNA repair, and regulation of the Cdc2 protein kinase. Telomere shortening was found in rad1, rad3, rad17, and rad26 mutants. Telomere lengths in previously characterized rad1 mutants paralleled the replication checkpoint proficiency of those mutants. In contrast, rad9, chk1, hus1, and cds1 mutants had intact telomeres. No difference in telomere length was seen in mutants affected in the regulation of Cdc2, whereas some of the DNA repair mutants examined had slightly longer telomeres than did the wild type. Overexpression of the rad1 ϩ gene caused telomeres to elongate slightly. The kinetics of telomere shortening was monitored by following telomere length after disruption of the rad1 ϩ gene; the rate was ϳ1 nucleotide per generation. Wild-type telomere length could be restored by reintroduction of the wildtype rad1 ϩ gene. Expression of the Saccharomyces cerevisiae RCK1 protein kinase gene, which suppresses the radiation and hydroxyurea sensitivity of Sz. pombe checkpoint mutants, was able to attenuate telomere shortening in rad1 mutant cells and to increase telomere length in a wild-type background. The functional effects of telomere shortening in rad1 mutants were assayed by measuring loss of a linear and a circular minichromosome. A minor increase in loss rate was seen with the linear minichromosome, and an even smaller difference compared with wild-type was detected with the circular plasmid.

The Caenorhabditis elegans Rad17 Homolog HPR-17 Is Required for Telomere Replication

“…Yeast 9-1-1 complex and Rad17 mutants display short telomeres, indicating that telomerase is functional but may be impaired (Dahlen et al 1998;Longhese et al 2000;Nakamura et al 2002). In contrast, C. elegans 9-1-1 complex and hpr-17 mutants display progressive telomere shortening phenotypes that result in sterility, suggesting a complete loss of telomerase activity in these mutants (Figure 3) Hofmann et al 2002).…”

“…The 9-1-1 complex was genetically identified in yeast as being required for checkpoint control in response to DNA damage (al-Khodairy and Carr 1992; Rowley et al 1992;Caspari et al 2000). Deletion of 9-1-1 complex subunits in yeast also results in short, stable telomeres (Dahlen et al 1998;Longhese et al 2000;Nakamura et al 2002). Chromatin immunoprecipitation analysis in Schizosaccharomyces pombe and mammals indicates that the 9-1-1 complex interacts with telomeric DNA (Nakamura et al 2002;Francia et al 2006;Verdun and Karlseder 2006).…”

“…In yeast, mutants deficient for Rad17 have short, stable telomeres. In addition, Rad17 associates weakly with telomeric DNA and has been suggested to act in the same telomere maintenance pathway as the 9-1-1 complex (Dahlen et al 1998;Longhese et al 2000;Nakamura et al 2002).…”

Role for the Silencing Protein Dot1 in Meiotic Checkpoint Control

“…In addition, analysis of telomeric silencing, telomere length and DNA repair revealed genetic interactions between mec3 and set1 mutants (Corda et al, 1999). In fission yeast, mutations in the rad26 ϩ , rad1 ϩ , rad17 ϩ , and rad3 ϩ checkpoint genes (the last three genes are homologs of S. cerevisiae RAD17, RAD24, and MEC1, respectively), result in telomere shortening (Dahlen et al, 1998) and, in the case of the rad3 mutant, reduced telomeric silencing (Matsuura et al, 1999). A mutation in MEC1 also leads to shorter telomeres (Ritchie et al, 1999) and impaired telomeric silencing (Craven and Petes, 2000).…”

Reconstitution and Molecular Analysis of the hRad9-hHus1-hRad1 (9-1-1) DNA Damage Responsive Checkpoint Complex

“…Second, additional studies in S. pombe indicated that spRad9, spHus1, and spRad1 interacted at very low stoichiometry, calling into question whether these proteins do indeed form a stable clamp (27). Third, there are phenotypic differences between sprad1 and sphus1 null mutants, which would be unexpected if the two proteins formed a portion of the clamp (38). To address these questions with the mammalian proteins and to characterize further the biochemical nature of hRad9, hHus1, and hRad1 complex, we examined the complex in human cell lysates using size-exclusion chromatography.…”