A SPACER PROTEIN IN THE SACCHAROMYCES-CEREVISIAE SPINDLE POLE BODY WHOSE TRANSCRIPT IS CELL-CYCLE-REGULATED

Monoclonal antibodies against the 110-kD component of the yeast spindl e pole body (SPB) were used to clone the corresponding gene SPC110. SP C110 is identical to NUF1 (Mirzayan, C., C. S. Copeland, and M. Snyder . 1992. J. Cell Biol. 116:1319-1332). SPC110/NUF1 has an MluI cell cyc le box consensus sequence in its putative promoter region, and we foun d that the transcript was cell cycle regulated in a similar way to oth er MluI-regulated transcripts. Spc110p/Nuflp has a long central region with a predicted coiled-coil structure. We expressed this region in E scherichia coli and showed by rotary shadowing that rods of the predic ted length were present. The 110-kD component is localized in the SPB to the gap between the central plaque and the sealed ends of the nucle ar microtubules near the inner plaque (Rout, M., and J. V. Kilmartin. 1990. J. Cell Biol. 111:1913-1927). We found that rodlike structures b ridge this gap. When truncations of SPC110 with deletions in the coile d-coil region of the protein replaced the wild-type gene, the gap betw een the central plaque and the ends of the microtubules decreased in p roportion to the size of the deletion. This suggests that Spc110p conn ects these two parts of the SPB together and that the coiled-coil doma in acts as a spacer element.