Pcp1p, an Spc110p-related calmodulin target at the centrosome of the fission yeast Schizosaccharomyces pombe

Abstract

In the budding yeast Saccharomyces cerevisiae, the calmodulin-binding protein Spc110p/Nuf1p facilitates mitotic spindle formation from the fungal centrosome or spindle pole body (SPB). The human Spc110p orthologue kendrin is a centrosomal, calmodulin-binding pericentrin isoform that is specifically overexpressed in carcinoma cells. Here we establish an evolutionary and functional link between Spc110p and kendrin through identification and analysis of similar calmodulin-binding proteins in the fission yeast Schizosaccharomyces pombe (Pcp1p, pole target of calmodulin in S. pombe) and the filamentous fungus Aspergillus nidulans. Like Spc110p and kendrin, Pcp1p and the A. nidulans protein contain predicted coiled-coil secondary structure and a COOH-terminal calmodulin-binding region. Green fluorescent protein fusions of Pcp1p localize to the SPB as analyzed by fluorescence and immunoelectron microscopy. Pcp1p overexpression causes chromosome missegregation, multiple mitotic spindle fragments, and multiple abnormal SPB-like structures, a phenotype remarkably similar to that of many human carcinoma lines, which exhibit chromosome and spindle defects, and supernumerary centrosomes.