Psc3 cohesin of Schizosaccharomyces pombe: cell cycle analysis and identification of three distinct isoforms

Cohesins are a group of proteins that function to mediate correct chromosome segregation, DNA repair and meiotic recombination. This report presents the amino acid sequence for the Schizosaccharomyces pombe cohesin Psc3 based on the translation of the cDNA sequence, showing that the protein is smaller than previously predicted. Interestingly, comparison of the amino acid and DNA coding sequences of Psc3 with fission yeast Rec11 meiotic region-specific recombination activator shows that both intron positioning within the genes and the amino-terminal half of the two proteins are highly conserved. We demonstrate that although the intergenic region upstream of the psc3+ start codon contains a consensus sequence for the cell-cycle regulatory MluI cell-cycle box, psc3+ transcription is not differentially regulated during the mitotic cell cycle. Finally, we demonstrate that an epitope-tagged version of Psc3 undergoes no major changes during the mitotic cell cycle. However, instead we identify at least three distinct isoforms of Psc3, suggesting that post-translational modification of Psc3 contributes to the regulation of cohesion function.