REGULATION OF TELOMERE LENGTH BY CHECKPOINT GENES IN SCHIZOSACCHAROMYCES-POMBE

We have studied telomere length in Schizosaccharomyces pombe strains c arrying mutations affecting cell cycle checkpoints, DNA repair, and re gulation of the Cdc2 protein kinase. Telomere shortening was found in rad1, rad3, rad17, and rad26 mutants. Telomere lengths in previously c haracterized rad1 mutants paralleled the replication checkpoint profic iency of those mutants. In contrast, rad9, chk1, hus1, and cds1 mutant s had intact telomeres. No difference in telomere length was seen in m utants affected in the regulation of Cdc2, whereas some of the DNA rep air mutants examined had slightly longer telomeres than did the wild t ype. Overexpression of the rad1(+) gene caused telomeres to elongate s lightly. The kinetics of telomere shortening was monitored by followin g telomere length after disruption of the rad1(+) gene; the rate was s imilar to 1 nucleotide per generation. Wild-type telomere length could be restored by reintroduction of the wild-type rad1(+) gene. Expressi on of the Saccharomyces cerevisiae RCK1 protein kinase gene, which sup presses the radiation and hydroxyurea sensitivity of St, pombe checkpo int mutants, was able to attenuate telomere shortening in rad1 mutant cells and to increase telomere length in a wild-type background. The f unctional effects of telomere shortening in rad1 mutants were assayed by measuring loss of a linear and a circular minichromosome. A minor i ncrease in loss rate was seen with the linear minichromosome, and an e ven smaller difference compared with wild-type was detected with the c ircular plasmid.