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The replication checkpoint (or 'S-M checkpoint') control prevents progression into mitosis when DNA replication is incomplete. Caffeine has been known for some time to have the capacity to override the S-M checkpoint in animal cells. We show here that caffeine also disrupts the S-M checkpoint in the fission yeast Schizosaccharomyces pombe. By contrast, no comparable effects of caffeine on the S. pombe DNA damage checkpoint were seen. S. pombe cells arrested in early S phase and then exposed to caffeine lost viability rapidly as they attempted to enter mitosis, which was accompanied by tyrosine dephosphorylation of Cdc2. Despite this, the caffeine-induced loss of viability was not blocked in a temperature-sensitive cdc2 mutant incubated at the restrictive temperature, although catastrophic mitosis was prevented under these conditions. This suggests that, in addition to S-M checkpoint control, a caffeine-sensitive function may be important for maintenance of cell viability during S phase arrest. The lethality of a combination of caffeine with the DNA replication inhibitor hydroxyurea was suppressed by overexpression of Cds1 or Chk1, protein kinases previously implicated in S-M checkpoint control and recovery from S phase arrest. In addition, the same combination of drugs was specifically tolerated in cells overexpressing either of two novel S. pombe genes isolated in a cDNA library screen. These findings should allow further molecular investigation of the regulation of S phase arrest, and may provide a useful system with which to identify novel drugs that specifically abrogate the checkpoint control.

Type

Journal article

Journal

J Cell Sci

Publication Date

03/1999

Volume

112 ( Pt 6)

Pages

927 - 937

Keywords

Amino Acid Sequence, Base Sequence, Caffeine, Cell Cycle, Checkpoint Kinase 1, Checkpoint Kinase 2, DNA Damage, Drug Resistance, Microbial, Fungal Proteins, Gene Library, Genotype, Hydroxyurea, Kinetics, Mitosis, Molecular Sequence Data, Phosphoprotein Phosphatases, Protein Kinases, Protein-Serine-Threonine Kinases, Ribonucleotide Reductases, S Phase, Schizosaccharomyces, Schizosaccharomyces pombe Proteins