Centrin/Cdc31p is a calcium binding protein related to calmodulin
found in the MTOCs of animals, plants and yeast. Its localization to
centrosomes suggests that centrin plays an as yet unclear but
important function at the centrosome. Cdc31p is required for SPB
duplication, but recent findings suggest that centrin also plays roles
elsewhere in the cell. To dissect the functions of Cdc31p, new
CDC31 alleles were selected only for temperature sensitivity,
but otherwise unbiased as to phenotype. Strikingly, ~80% of the
mutations mapped to the C-terminus. Two known phenotypes of
cdc31, G2/M arrest and lysis were not correlated, suggesting
that the mutations affect interactions of Cdc31p with different
proteins. Alleles causing high G2/M arrest map to the C-terminus,
suggesting that this region affects an SPB-related function. These
alleles showed genetic interactions with kar1-delta17
suggesting that the C-terminus is specific to KAR1's SPB
function. Alleles causing a high lysis defect map to the middle of the
protein, indicative of disruption of a kic1-like
function. Mutations in the middle of the protein had reduced Kic1p
kinase activity, suggesting that this region activates
Kic1p. Mutations in two C-terminal regions disrupt binding of both
Kic1p and Kar1p, suggesting that these regions form a ligand-binding
surface on Cdc31p. The new CDC31 alleles give us insight into
the function of the protein and will be used in genetic screens to
identify new CDC31 interacting genes.
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