Fig. 1. Fission yeast Mek1 belongs to the family of Cds1/Rad53/Chk2 checkpoint kinases and is expressed only in meiotic cells. (A) Alignment of the protein sequences of S. cerevisiae Mek1 (ScMek1), S. pombe Mek1 (SpMek1) and S. pombe Cds1 (SpCds1). Identities are highlighted in black and conservative substitutions in gray. Numbers at the left represent amino-acid positions. Alignment and shading were performed with ClustalW 1.8 and Boxshade 3.21, respectively, at the BCM Search Launcher (http://searchlauncher.bcm.tmc.edu/). (B) Phylogenetic tree of the family of FHA checkpoint kinases. The clustal method with PAM250 residue table was used. Sp, S. pombe; Sc, S. cerevisiae; Mm, M. musculus; Hs, H. sapiens; Xl, X. laevis; Ce, C. elegans. A schematic representation of the functional motifs in this protein family (with the exception of Rad53, which contains two FHA domains) is shown. (C) PCR amplification of S. pombe mek1⁺ using primers mek1-N and mek1-C (small arrows; see Materials and Methods). The following DNA templates were used: cDNA from vegetative S. pombe cells (Veg), cDNA from meiotic cells (S964) at 2 hours and 3 hours in meiosis (Mei 2h and Mei 3h, respectively) and S. pombe genomic DNA.

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