S-pombe cdc11p, together with sid4p, provides an anchor for septation initiation network proteins on the spindle pole body

Background: The signal for the onset of septum formation in the fission yea st Schizosaccharomyces pombe is transduced by the septation initiation netw ork (SIN). Many of the components of the SIN are located on the spindle pol e body during mitosis, from where it is presumed that the signal for septum formation is delivered, Cdc11 mutants are defective in SIN signaling, but the role of cdc11 in the pathway has remained enigmatic. Results: We have cloned the cdc11 gene by a combination of chromosome walki ng and transfection of cosmids into a cdc11 mutant. Cdc11p most closely res embles Saccharomyces cerevisiae Nud1p and is essential for septum formation . Cdc11p is a phosphoprotein, which becomes hyperphosphorylated during anap hase. It localizes to the spindle pole body ;at all stages of the cell cycl e, in a sid4p-dependent manner, and cdc11p is required for the localization of all the known SIN components, except sid4p, to the SPB. Cdc11p and sid4 p can be coimmunoprecipitated from cell extracts. Finally, like its S. cere visiae ortholog Nud1p, cdc11p is involved in the proper organization of ast ral microtubules during mitosis. Conclusions, We propose that cdc11 p acts as a bridge between sid4p and the other SIN proteins, mediating their association with the spindle pole body .