Sister chromatid cohesion is essential both for alignment of chromosomes at metaphase and for DNA repair in G2 phase. Cohesion is maintained by the multiprotein complex cohesin and cohesin-associated proteins, such as Pds5. Present in S. cerevisiae, A. nidulans and metazoans, Pds5 is implicated in establishment and maintenance of chromatid cohesion; however, its importance and precise role have proven difficult to define. Chris Norbury and co-workers have therefore characterized the Pds5 orthologue from the model organism S. pombe. They find that, unlike S. cerevisiae Pds5p, S. pombe Pds5 is non-essential and is not required for chromosome condensation. Nevertheless, it does appear to function in chromatid cohesion: the authors provide genetic and biochemical evidence for interaction between Pds5 and cohesin components such as Rad21; in addition, they find that pds5 mutants exhibit high levels of chromosomal abnormalities and that Pds5 becomes essential if mitotic progression is delayed. S. pombe Pds5 thus appears to have an important role in chromatid cohesion but one that differs significantly from that of S. cerevisiae Pds5p.
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