An analysis of the role of the Schizosaccharomyces pombe homolog of survivin, Bir1p, in mitosis

Abstract

The chromosome passenger complex, consisting of Aurora B kinase, Survivin and INCENP, has been shown to be important for a variety of processes in mitosis and cytokinesis. The exact mechanisms by which this complex executes its various functions are in the process of being unraveled. This study describes the analysis of the Schizosaccharomyces pombe homolog of Survivin, Bir1p. bir1+ is essential for cell viability. Analysis of bir1 conditional mutants revealed that Bir1p is essential for maintaining mitotic chromosome architecture, possibly by recruiting the S. pombe Aurora B kinase, Ark1p, to kinetochores at the onset of mitosis. Bir1p is also important for coordinating anaphase A to B transition, as well as for spindle elongation in anaphase B. Possibly, the various functions of Bir1p are dictated by its cellular location. Bir1p, a nuclear protein, relocates from kinetochores to the spindle mid-zone at anaphase A to B transition. This relocation requires cyclin B proteolysis, intact microtubules and the plus-end motor, Klp5p. Although minimal exchange of Bir1 protein sub-units occurs between the spindle and the nucleoplasm, Bir1p redistributes laterally within the mid-zone region. Thus, Bir1p dynamics differs from that of tubulin on an anaphase B spindle. The novel dynamic behavior of Bir1p at the spindle mid-zone suggests that the process of spindle elongation and stability is based on overlapping dynamic properties of many components.