Phosphorylation of T238 site of Cdc5 is dispensable for cell viability. (A) An alignment of activation segment loops (T-loops) in diverse polo-kinases, showing the conserved T238, T242 and L251 residues of the ScCdc5. (B) Viability of the strains Y505 (cdc5-1), Y1327 (cdc5-1<empty vector>), Y1329 (cdc5-1 <CDC5::3xHA>), Y1331 (cdc5-1 <CDC5-N209A::3xHA>), Y1333 (cdc5-1 <CDC5-T238A::3xHA>) and Y1461 (cdc5-1 <CDC5-T242A::3xHA>), at different temperatures. Exponentially growing cell cultures were serially diluted (1:10), and each dilution was spotted on SC-Trp plates. Plates were incubated 3 d at the indicated temperatures.