The Schizosaccharomyces pombe dim1(+) gene interacts with the anaphase-promoting complex or cyclosome (APC/C) component lid1(+) and is required for APC/C function

The Schizosaccharomyces pombe dim1(+) gene is required for entry into mitos is and for chromosome segregation during mitosis. To further understand dim 1p function, we undertook a synthetic lethal screen with the temperature-se nsitive dim1-35 mutant and isolated lid (for lethal in dim1-35) mutants. He re, we describe the temperature-sensitive lid1-6 mutant. At the restrictive temperature of 36 degrees C, lid1-6 mutant cells arrest with a "cut" pheno type similar to that of cut4 and cut9 mutants. An epitope-tagged version of lid1p is a component of a multiprotein similar to 20S complex; the presenc e of lid1p in this complex depends upon functional cut9 lid1p-myc coimmunop recipitates with several other proteins, including cut9p and nuc2p, and the presence of cut9p in a 20S complex depends upon the activity of lid1(+). F urther, lid1(+) function is required for the multiubiquitination of cut2p, an anaphase-promoting complex or cyclosome (APC/C) target. Thus, lid1p is a component of the S. pombe APC/C. In dim1 mutants, the abundances of lid1p and the APC/C complex decline significantly, and the ubiquitination of an A PC/C target is abolished. These data suggest that at least one role of dim1 p is to maintain or establish the steady-state level of the APC/C.