14-3-3 Protein Homologs Required for the DNA Damage Checkpoint in Fission Yeast

Abstract

During the cell cycle, DNA is replicated and segregated equally into two daughter cells. The DNA damage checkpoint ensures that DNA damage is repaired before mitosis is attempted. Genetic studies of the fission yeast Schizosaccharomyces pombe have identified two genes, rad24 and rad25, that are required for this checkpoint. These genes encode 14-3-3 protein homologs that together provide a function that is essential for cell proliferation. In addition, S. pombe rad24 null mutants, and to a lesser extent rad25 null mutants, enter mitosis prematurely, which indicates that 14-3-3 proteins have a role in determining the timing of mitosis.

Chk1 complements the G2/M checkpoint defect and radiosensitivity of ataxia-telangiectasia cells

“…Overexpression of chk1 in wild type S. pombe led to cellular elongation and a failure to enter mitosis (Al-Khodairy et al, 1994;Ford et al, 1994). This was the same phenotype as observed with a number of radmutants suggesting that these function upstream of chk1 in checkpoint arrest (Walworth and Bernards, 1996).…”

“…In S. pombe several mutants have been described that are unable to arrest the cell cycle in response to DNA damage at the G2 checkpoint (Weinert and Hartwell, 1990;AlKhodairy et al, 1994;Ford et al, 1994). One of these genes, chk1, encodes a protein kinase that appears to function downstream of all other checkpoint genes to elicit a cell cycle arrest via cdc25 and wee1 to maintain tyrosine phosphorylation of p34 cdc2 (O'Connell et al, 1997;Rhind et al, 1997;Furnari et al, 1997;Sanchez et al, 1997).…”

“…Further, the human chk1 homologue (hchk1) is capable of phosphorylating cdc25 on a serine residue (S216 for cdc25C), which results in association of cdc25C with 14-3-3 proteins throughout interphase (Peng et al, 1997;Sanchez et al, 1997). In this state, the 14-3-3 bound cdc25C is inactive (Ogg et al, 1994), 14-3-3 proteins also interact with wee1 (Honda et al, 1997), and are required for both normal G2 control and response to chk1 overexpression (Ford et al, 1994). Thus chk1 may signal through both wee1 and cdc25, possibly in¯uencing interactions with 14-3-3 proteins, and lead to a maintenance of inhibition of p34 cdc2 for the duration of a checkpoint arrest.…”

Yeast 14‐3‐3 proteins

“…Simultaneous rad24 rad25 disruption is lethal. 14 The genes play a role in timing of mitosis and are essential for cell cycle arrest in response to radiation-induced DNA damage. 14 This effect is probably mediated through Cdc25p.…”

“…Best studied are the 14-3-3s in baker's yeast, but genes encoding these proteins have also been reported for Schizosaccharomyces pombe, 14 Candida albicans, Trichoderma harzianum and Lentinus edodes. 25 Saccharomyces cerevisiae and Sz.…”