The COP9/signalosome complex is conserved in fission yeast and has a role in S phase

The COP9/signalosome complex is conserved from plant to mammalian cells. In Arabidopsis, it regulates the nuclear abundance of COP1, a transcriptional repressor of photomorphogenic development [1,2]. All COP (constitutive pho tomorphogenesis) mutants inappropriately express genes that are normally re pressed in the dark. Eight subunits (Sgn1-Sgn8) of the homologous mammalian complex have been purified [3,4]. Several of these have been previously id entified through genetic or protein interaction screens. No coherent model for COP9/signalosome function has yet emerged, but a relationship with cell -cycle progression by transcriptional regulation, protein localisation or p rotein stability is possible. Interestingly, the COP9/signalosome subunits possess domain homology to subunits of the proteasome regulatory lid comple x [5,6]. Database searches indicate that only Sgn5/JAB1 is present in Sacch aromyces cerevisiae, precluding genetic analysis of the complex in cell-cyc le regulation. Here we identify a subunit of the signalosome in the fission yeast Schizosaccharomyces pombe through an analysis of the DNA-integrity c heckpoint. We provide evidence for the conservation of the COP9/signalosome complex in fission yeast and demonstrate that it functions during S-phase progression.